Bug Description:
When loading a pre-1.5.28 savegame post-1.5.28, adding new constructions of any type from the construction menu (bottom-left panel in system view) will add to the top of the queue rather than the end (bottom), without Alt being pressed. This is only true for the construction menu, and not any other source (including planet specialization or anomolies) - those work fine. What happens when Alt is pressed is unknown, as I didn't get the opportunity to test it.

This bug only happens once across all savegames while the game is installed (even if you stop the program and re-enter to use another pre-1.5.28 savegame). Reinstallation or reverting to Older Versions has not been tested.

Fix:
Alt+Tab out of your current game at any time and in any view. I did it in Borderless Fullscreen but I'm assuming the window format doesn't matter. Then, Alt+Tab back in and it should be fixed. Alternatively, if you don't have any other programs running, you can Save your game, exit to the Main Menu, then Load that save or a different one of your liking. It should be fixed across all savegames.

Steps to Cause (But Not Reproduce):
0. Have Endless Space 2 already installed pre-1.5.28 and update the game through Steam. Also install the 'Awakening' DLC during this time. All other DLC pre-installed.
1. Open the game and Load up a savegame from before 1.5.28 for the first time after 1.5.28.
2. Enter the System View of any system with a pre-existing construction queue.
3. Select any available construction from the Construction Panel/Menu. Do not press/hold Alt or its replacement key if customized. (Bottom-left corner panel only. Any size.)
4. Watch the construction be added to the top of the queue rather than the bottom.
5. Repeat at will in any system until the provided fix is implemented.

Reproducibility: Once
Considering the provided fix is implemented across all save games (I checked - even the old ones), I wasn't able to reproduce the glitch. There areas that I'm aware that I haven't checked, but to be honest I'm kinda lazy. This is what I haven't checked (that I'm aware of):
1. Generating a new unsaved galaxy.
2. Uninstalling the game and reinstalling. At all.
3. Reverting to a previous version. That includes making new saves there and re-updating.
4. Uninstalling the 'Awakening' DLC (purchased+installed pre-1.5.28 but after my most recent savegame).
5. Playing on another computer (obviously).
6. Whether holding Alt (or alternate) fixes the bug as well, or has other effects.

Expected Behavior:
When selecting a construction from the menu, the construction is supposed to enter the queue from the end (bottom), when not holding Alt.

Yes, I'm sure that I wasn't holding Alt, the key didn't look pressed (my only lifted hand was on the mouse), I don't have any customized controls (including on my hardware other than Mouse4 & Mouse5 being disabled). There was no lag throughout the entirety of the glitch so I doubt the input would've lagged, plus I don't use Alt for anything in-game.

Version:
Current/Used: V1.5.28 S5 GOLD-Public
Tested Savegame Saved-Version: Likely 1.5.11, definite version unknown.
'Awakening' DLC Installation Version: V1.5.11 S[?] GOLD-Public (DLC Unplayed)

Notes:
- I switched from Fullscreen to Borderless Window after entering the game. I had not attempted to add any constructions to any queues yet. I made no other window changes.
- I played the game some hours after my computer had crashed due to the GPU overheating from "Hardspace: Shipbreaker" and its Early-Access-ness. My GPU & PC ran fine in-between.

I don't have this issue. Are you sure you simply didn't have your Alt button stuck?

Salterius wrote:

It is Alt-Tabbing that can cause this sometimes, simply pressing Alt once resolves the issue.

Huh, well I guess the bug exists - just not in the form I had thought. I'll leave the thread up in case anyone else experiences the bug. Although unnecessary, the solutions I offered work if anyone is too lazy to scroll down to your reply. I couldn't find any duplicates of the topic, so hopefully this thread doesn't just work to clutter the forum.