Sounds like a "dreadlock" issue. They did change how thread locks work between 7.2 and 7.5, in particular rendezvous timeout. The bug is likely in your code, not accounting for dreadlocking.
To pinpoint, pepper your code liberally with print statements - don't be frugal on them electrons. Before field assignment, after field assignment - carpet bomb that code. And btw, the remote reboot combo (HHHHHU<<>>) should work.
When i get in a pickle like that, i don't even bother with proper texts - it will be removed - i just do "? 1", "? 2" and so on. I tend to bisect - add more diagnostic as i zero-in on the exact place... there are infinities of numbers between 1 and 2 (meet the Dewey library classification
- 1.5, 1.3, 1.4, 1.45...
Keep us posted on the discovery/