Aaaaalright... just spend an hour on the phone wth the German SEN line (btw, I was too stupid yesterday... didn't realize I dialed the Swedish number, not the German one as I just used the "contact SEN Service link" in the app....) to figure out what is going on.
So, the agent had also no idea why the segment got cancelled. She then talked to the ticketing desk for a loooooong time. And they had no idea why it is cancelled either. Just that the German Bahn REFUSED to ticket the segment and therefore the system marked it as "Cancelled". While it was confirmed and ticketed from LH to me. After some more investigation, it seems that DB expects the train to run over capacity in 2nd class and therefore suddenly decided they will only sell 1st class tickets on that connection:
Which was DEFINITLEY not the case when I looked up the connection yesterday.
Anyhow, the M&M agent couldn't offer ANY alternative train connection. Even though, they run every hour, e.g.:
She suggested I have two options:
1) Cancel and refund the whole trip
2) Only go to FRA and then book a Rail+Fly Ticket for 35 EUR and just hop on any train available.
Option 1) was definitely out of question and even for 2) I don't see why I should do this as I will not get those precious 20 points and also I don't want to fight with some nasty Bahn conductor over "if can enter a full train or not". So I pushed back and told her it is LH's problem to figure out, not mine. I did suggest LH 160, which yesterday had a lot of availability but today.... all gone. Guess same thing happened to a few more people. She then suggested to rebook on LH833 and LH 158. Which even though it makes for a kind of nasty morning to get to CPH that early... works for me better than anything later in the day and don't even need to cram into those nasty trains from FRA. She then asked ticketing for approval to rebook me on those and got an ok after a few more minutes wait.
So, all good now. But man... what a mess. For such a small thing. And why didn't that **** chatbot offer any rerouting in the first place? It could have put me on LH 160 already 2 days ago but insisted "all is ok with my flight". And when I asked it "what about the train LH3734" alsways said "sorry, I do not understand your question. And the real agent it connected to me also did NOTHING at all. He just said "new flights will appear at some point".
Rather frustrating.