Likely you need to use the "divide and conquer" approach. Make a copy of the project. Delete half the topics from the copy and try compiling. You work your way through deleting and compiling until you isolate the problem topic(s).
Another approach would involve taking the good copy, then adding perhaps five topics at a time and compiling until you isolate the culprit(s).
This is exactly what I have been doing so far. No-no-no, I don't want to do this. There are 3K files per project on average... and there are 20 projects x 7 languages... you get the feeling. There must be a better way.
If you do find a better way, please post it here so we can all benefit from it.