This exact thing is happening to me since yesterday. It comes back to life when I throw the whole session away.

i was having this issue yesterday. the same prompt would send it into a loop where it would appear to be doing nothing for 30+ minutes until i cancelled it. it would show 400 tokens used and thats it. I tested on a previous version (2.1.68) and it still ran into this neverending loop BUT at least the token count kept steadily increasing.

So we are seeing 1. some sort of model degredation is my guess (why it can't break a thinking loop on some problems), as well as 2. a clear drop in thinking token UI transparency

when i left it running overnight it finally sent a message saying it exceeded the 64000 output token limit