Periodically. I don't know if there's a pattern or not, or even if there has been, whether they will follow it in the future. You'd have to scour the UA card thread to figure that out (there'll obviously be posts and discussion aplenty from each time the 50k "open" offer has appeared).

But IMHO the key is not to try to predict when, but simply to know which cards do repeat higher bonuses, and then wait until the higher bonus re-appears before you apply.

You can never know that you got the very highest bonus (for example, over at Citi, the Hilton HHonors no-AF Visa was usually 40k or 50k while it was easy to churn fast, then a 60k offer appeared a couple time, and then right after "fast churning" was shut down last weekend, a 75k offer appeared, which no one ever expected.

But in the case of the UA bonus, it's been known for years that 50k was a periodic offer open to all*, so if you had just researched that much, you could have waited until that higher offer appeared before applying. Your mistake seems to have been not being aware (at the time you applied for the smaller offer) that there were occasionally much bigger offers.

* The UA bonus is always 50k for those with UA elite status. So when reading reports of UA 50k, you have to factor out the offer for those with status if you have no status at UA.

It's a general rule that the most widely publicized offers for airline and hotel cards are often not the best offers. You have to research each card you're thinking of applying for on FT and figure out what the best offers are that are known for that card.

Meanwhile, all the threads from the past on these cards are archived on FT. So all the information you seek by asking in this thread is already out there somewhere; you just have to figure out how to find it efficiently.