I was able to test it fairly quickly and eliminate the UI mods I had running, the ACU build menu bug I mentioned to you is an interaction with BrewLAN. When I enabled that mod, the problem occurred. (to recap, the issue was when Tech upgrading the ACU the ACU build menu became stuck on screen even if you select another unit, in single player it was solved by saving and restarting the game, it also was only with Tech upgrade - RAS, Shield etc didnt do this).
Here is the link to the mod in question, ie this is where the author loads the current version: https://github.com/The-Balthazar/BrewLAN
EDIT NOTE: I tested this with just BrewLAN 7.5 (latest release) and Notify 3.7 running and it did have the same issue. Going to get 3.8 and see if the same thing happens, but on my computer it definitely occurs with just the 2 mods running sans all else.
Second Note: The latest version of Notify showing up from a Server Search in the Vault is 3.7 - I had heard there are some issues with some mods not being accessible in the Vault though they are in there. Reference this thread - viewtopic.php?f=41&t=11470