What does this refer to? Tried to enter unprintable character: 8

I understand I am playing a massive game. Ludicrous Map, 100 Civs, 2.8.

However, I can continue playing the game, turn after turn without problem, but when I save it, this error freezes my game and then crashes it. Im stuck at save on turn 163. I can continue for a dozen turns and eliminate more than five Civs from the game which is down to 70 something now but when I try to save it this error occurs in my debug file. It is the only thing there after saveloadwnd, if I do a hard turn off on the computer when it is frozen.

These are my last 6 debug messages, blue is the save which then freezes the game.

DebugMessage:  Tried to enter unprintable character: 8
DebugMessage:  Tried to enter unprintable character: 8
Debug Message:  CSaveShipDesignWndMsgData::OnPressSave: shipType: 0, isPlayerMade: 1
Debug Message:  Popup Manager Update: Unhiding GameMenuWnd
Debug Message:  Popup Manager Update: Unhiding SaveLoadWnd
DebugMessage:  Tried to enter unprintable character: 8