When I merged a forum from a different software my database encoding was different than UTF8. I ran the tool to convert all tables to utf8 and the cache for forums became empty. Even rebuilding the cache doesn't work nor does deleting the forum cache in the database actually make it generate correctly. To get it back, I had to run the Recount and Rebuild tools. Definitely something strange is going on there.
Did you use the latest github build for this matter or 1.8.3?
Not sure why the cache shouldn't work anymore. Also not sure why Recount & Rebuild fixed it. Though the cache uses data that would mean that the conversion broke the counters.
I thought you used a development version from github, which at some point had problem with cache serialization, that's why I asked about the version earlier. If you used a clean package, it wasn't that.
Anyways, I can't reproduce in a clean install, the cache is never empty for me. Never seen any similar support thread either. I guess it's connected with merging from another software, so perhaps it should be moved to merge support, where all the other issues connected with merge are reviewed?
It's pretty sure not related to the merge system as it hasn't anything to do with it. There were issues with the counters but the merge system does nothing that could break the UTF-8 Conversion.
Well, here's something similar, not sure if related:
http://community.mybb.com/thread-164285.html
But if you don't think it's merge, I'll reject it since it's not the core either, unless it's some kind of a rare hard-to-track bug with one of the fields breaking the cache on saving or something like that. If anyone has more info, like steps to reproduce with(out) using the merge system, feel free to share.
EDIT: UTF-8 conversion doesn't even seem to affect any cache directly:
https://github.com/mybb/mybb/blob/featur...p#L170-701 No idea why would the cache become empty immediately after running it.
The linked issue was simply, that the forums didn't have a parent category which is a known issue but not related to the encoding.