I recently flew out of Rome Ciampino on a 06:15 flight, and I experienced perhaps the most disorganised / out-of-sync check-in process there, which almost led me to miss my flight. The airport is closed all night and opens up at 04:30 by when there are many passengers accumulated outside queuing to go inside, followed by a single common check-in line for all flights regardless of departure time. I personally got to the airport around 04:45 and found myself queuing quite far back on the check-in line. The first 4 flights (including mine) were at 06:00, 06:10 and 2 flights at 06:15 with the rest following from 06:25 onward. Needless to say, the queue was not based on departure time, it was a mix of passengers including later departures.

The queue was originally moving at a reasonable pace but by 05:30 as we approached the first departure.time, a couple of check-in staff moved to different check-in desks and formed their own queue for a supposedly rapid check-in for the first 2 departures, and then 5-10 mins later asked passengers for the next 2 departures to move to that queue, which wasn't moving particularly rapidly and still had passengers for the first 2 departures on there. I actually would have been through security by the time I did check-in via the "rapid" queue, if I had just been able to stay in main queue.

The check-in agent spent more than 5 mins on 1 passenger with a seemingly complicated issue, and there was growing chaos and frustration behind, including me. I even got the attention of the agent briefly and asked if the flights will wait for us to complete check-in, and he said "I don't know, I am just 1 person dealing with all of you". I had already seen a passenger for the 06:00 in the "rapid" queue who got to the front around 05:45 only to be told his flight had already closed. I have to admit I took advantage of a bit of the resulting chaos and pushed through to complete my check-in, and just about made it through security and to my flight, which thankfully was just outside the gate. Less than 5 mins after I entered the plane, the doors closed, so quite a close call.

I'm left wondering if this may be an intentional tactic to have some people miss their flights and therefore spend more money on new flights. Would Ryanair re-book people to the next flight free of charge and pay for interim accommodation, especially considering that the flight was only missed due to their insufficient capacity / organisation at check-in?

I doubt this is intentional, but it's definitely in line with the "allocate the least resources possible to anything to save on cost" Ryanair modus operandi. They simply didn't have enough check-in staff for the number of passengers.
This happens at other airports with other airlines as well (picture HKT where authorities set up extra screening of all passengers and bags to just enter the departure hall), but I`ve always been accommodated without having to buy a new ticket in such cases.
If you would have missed the flight despite being at the airport by the time check-in opened and they failed to check you in on time because there wasn't enough staff, and they made you buy a new ticket, be prepared to drag Ryanair to court to get your money back.

How long before departure do they advise you to arrive at the airport?

Contrary to other airlines, Ryanair does not specify this. We recommend that you check-in baggage as early as possible is what they have to say about this.
But here comes the big one: The Bag Drop desks open two hours prior to the scheduled flight departure time. At CIA, that is obviously not the case if the airport only opens at 4:30 and the flight departs at 6:15. They aren't adhering to their own published policies which any customer can reasonably expect to be in place at any airport for any flight.
If they tried to make someone buy a new flight at walk-up prices after one missed their original departure because of Ryanair opening check-in too late - well, I�d say you'd have no problem at all to prove this in court and get that money back
See https://help.ryanair.com/hc/en-us/ar...ort-Timeframes

More recently with Covid checks in place, I think they have specified arriving 2:30 before departure, which of course is meaningless for CIA earliest departures. In any case, with so many flights congested together with a shorter check-in window (e.g. 1:30 for the 06:00 flight) and no proper queuing of passengers by departure time, e.g. some 06:00 could be far behind in the queue due to 07:00 or later departure passengers also rushing in to check-in early (rightfully too to avoid stress), it is just pure risk. A queue is a queue regardless of departure time, and one couldn't possibly jump it, which I think is the root cause of all the troubles in absence of Ryanair having the capacity to comfortably clear the queue promptly. The last moment realisation that there are still passengers not checked-in close to flight departure times, and sending them to a separate dedicated (but slower) queue causes even more chaos. I also saw a lot of side-ways conversations among check-in agents and the only time the one on the dedicated queue showed some urgency was when he (without empathy) informed the 06:00 passenger in the queue that the flight had already closed. Is it lack of motivation? Or financial incentives from extracting extra revenues? Something is definitely off from what I observed there!

Can't help but feel it's all on purpose, yet another high-cost trap to compensate for the low-cost flight!

Italy ... What do you expect?

Used to be 2h, but unsure now

ryanair.com still says 2 hours - see: https://help.ryanair.com/hc/en-gb/ar...ort-Timeframes

The mails they send out in German say 2.5 hours "Bitte stellen Sie sicher, dass Sie mindestens 2,5 Stunden vor Ihrem Flug am Abflughafen sind und alle obligatorischen Reisedokumente f�r die Kontrolle bereit haben."

Who on earth arrives airport 2� hours before a FR flight (in particular if handlugage only)...

Same in English in two emails prior to a flight from ACE earlier this week.

"Please ensure that you arrive a minimum of 2.5 hours prior to departure and have all mandatory travel documents prepared, ready for inspection at your departure airport."

People who want to make sure the aircraft doesn't leave without them. You can always kill extra time at the airport but it's hard (and stressful) to try to make up lost time if you are late or there are unexpected delays.

Agreed - I want a relaxed experience and usually a drink or two. No way I'm cutting it short if I can help it.

I see, interesting. I always try to minimize wasted time at the airport but I suppose each to their own.

It's only wasted if you choose to waste it. I've always found or planned something to do. Even having a nap is not a waste of time.