sqlite does not support declaring the length of integer based columns e.g. int(9) or bigint(30). They need to be replaced with int / bigint.
That's why we said "don't update" - the whole upgrade is still not tested. There are some bugs especially the theme update isn't working.
Don't update seems to be a good idea especially when working on an update issue
https://github.com/mybb/mybb/issues/611
Seriously I crash my development installation all the time, so this was just a fyi report... had to fix the bug anyway to test my (currently not working

) fix

Setting this to pushed as we have an issue for this.