Welcome Dm1tre:

The stuck in flight may have an issue somewhere with mercenaries, but not in this case.  I never use mercenaries. There were no mercenaries. It is specific to the Spectre, all other ships I have encountered work fine.

Yep, mercenaries bugged. Reloaded save about million times.

So when you as mercenaries w/o "Privateer" active enter system guarded by pirate flee, they will not attack you this turn. Three possible ways.

• If you attack them and win, next battle will be stuck with AI choosing tactic.
• If you attack them and lose, game is ok.
• If you dont attack them and end turn (you cant leave, cause they guard system), they will attack you next turn with AI stuck.

If you as mercenaries w/ "Privateer" active enter system guarded by pirate flee, they will not attack you, nor you can attack them, until its your home system and you can set off "Privateer". Three possible ways further.

• You stay in the system and end turn. Game bugged.
• You enter system and leave before turn ends. Game ok.
• You pass by w/o parking in system. Game bugged.

This bug can also cause  million posts of "Stuck at fight. Stuck at turn end." Cause AI can also hire mercenaries. And if AI stuck at fight choosing tactics, nor u can end turn or right them cause they choosing tactics.