I loaded a game and got this error message:

[Gameplay] The contract contains an empty option (state: Proposed).
--------------------------------------------------------------------------------
at ChangeDiplomaticContractStatePreprocessor in :line 0
at InternalInvoke in :line 0
at Invoke in :line 0
at Invoke in :line 0
at Preprocess in :line 0
at ProcessOrders in :line 0
at UpdateMessageBoxAndProcessOrders in :line 0
at Update in :line 0
at Update in :line 0
at Update in :line 0
at LateUpdate in :line 0

--------------------------------------------------------------------------------
V0.1.21 S0 ALPHA-Public (64-bit)

It let me continue though.  And then I noticed that all four of my Hero Ships had defaulted back to basic white modules!

Thank you for reporting this, but ... you're posting in the wrong forum. This is the Endless Legend forum ^^

Please try posting here : https://www.games2gether.com/endless-space-2/forum/114-bug-reports

Also, could you also please upload the savegame file which you tried to load? That would allow the devs to repro the issue quicker.