about 1 year ago - AndrewT - Direct link
A saved game from several years ago will not work properly under the current game version, there have been too many major changes since.

To continue it you'd need to revert to the game version you last played it under. You can see what game version was released when here:

Patches - Stellaris Wiki

stellaris.paradoxwikis.com stellaris.paradoxwikis.com
To revert you go into the Steam Betas tab for this game. And as you are going back several versions, it would be best to delete everything in the Documents/Paradox Interactive/Stellaris folders (except valued saved games) so the older game version can write those files as it wants to.

Good luck!