As reported in https://www.games2gether.com/endless-space-2/forums/114-bug-reports/threads/28344-random-ui-freeze?page=1

Basically the game UI freezes, but you can still interact with it. E.g. clickin the End Turn button makes the sound for end turn, and rolls it over. Happens on a consistent basis with the save file, after one or two turns. Basically makes it unplayable. To reproduce, play the game as normal, manage all of the activites (it may be based on windows opened).

Diagnostics - 2018'02'10 @1207'06''.zip

AutoSave 267.sav

DxDiag.txt

Version V1.2.8 S5 GOLD-Public

Tried to reproduce the bug in the last two hours - no occurrence. Heisenbug?

Happened quite a few times again while playing multiplayer - luckily the rejoining works just fine. What other information could I collect?