And so, I have discovered the cause of our crashes on both the change of year, as well as at the start of summer. In the current iteration of the save I have created, I have allowed time to pass for five years without any form of crashing, freezing, or instability. As far as I can tell, the problem has been solved and Orid Xem has been saved (from my own hands).
Regarding the issue; it appears that it was exclusively related to Silverthrone, specifically position assignments. More specifically, military position assignments. At some point during my turn, or perhaps even before, a few of the assignment IDs for squad commanders were thrown off by about two positions. This was enough to have multiple histfigs be pointed to as the leader of multiple different squads or even overlapping simultaneously. Due to this, using the ingame UI to change squad leaders or nobles crashed the tick after they were used, no doubt due to the strangeity of that overlapping data. I have used gui/gm-editor to rectify that specific issue, and from my internal testing, it was the sole cause of the problem.
For your viewing displeasure, here are some notes thereon that will probably not have any value to you.
SQUADS
728 - Bridgemen
leadAss - 11
currentOcc - 118224
ID'S MATCH-UP
729 - NE Towermen
leadAss - 12
currentOcc - 124324
ID'S MATCH-UP
730 - Gateguards
leadAss - 13
currentOcc - 118248
ID'S MATCH
731 - SE Rivermen
leadAss - 14
currentOcc - 118170
histFig did not have Entity Link assignment, FIXED
732 - S Outer Towermen
leadAss - 12 (SAME AS NE Towermen!!)
currentOcc - 118198 (Has tons of former positions as ass 12, and also currently assigned as 12 in their links. Despite 124324 correctly assigned in entity positions. Due to this number being skipped, it screwed the rest of the squads)
Fixed by changing 118198's position assignment to be 34, and fixed the squad and their military data accordingly.
733 - S Towermen
leadAss - 15
currentOcc - 118199 (Does not have entity links, has been assigned to position 15, as the rest of the data suggests should be.)
734 - Inner Gateguard
leadAss - 16
currentOcc - 118160 (Currently linked to position 14 rather than 16.)
Fixed by setting fig's assignment to 16.
735 - Highest Tower
leadAss - 17
currentOcc - 118195 (Linked to position 15 rather than 17)
Fixed by setting fig's assignment to 17
736 - NE Rivermen
leadAss - 18
currentOcc - 118234 (Linked to position 16 rather than 18)
Fixed by setting fig's assignment to 18
737 - SE Inner Towermen
leadAss - 19
currentOcc - 118235 (Linked to position 17 rather than 19)
Fixed by setting fig's assignment to 19
738 - E Inner Towermen
leadAss - 20
currentOcc - 124089 (Currently this figure is travelling, may need to circle back and change them out for another histfig)
ALL ID'S MATCH
739 - NE Inner Towermen
leadAss - 21
currentOcc - 118230 (Linked to position 19 rather than 21)
Fixed by setting fig's assignment to 21
740 - Inner Castle Guard
leadAss - 22
currentOcc - -1 (Does not have a leader, previous leader seems to have died in 927, will fill position after fixing rest.)
newOcc - 124292
741 - River Gateguard
leadAss - 23
currentOcc - 118247 (Linked to position 21 rather than 23)
742 - Gate Towermen
leadAss - 24s
currentOcc - 118168 (Currently dead, but was still somehow considered a squad occupant and has position in the entity assignments. squad needs a new leader)
newOcc - 124281
743 - Fieldsmen
leadAss - 25
currentOcc - 118283 (Linked to position 23 rather than 25)
807 - Realmsmen I
leadAss - 26
currentOcc - 124260
ID'S MATCH
808 - Realmsmen II
leadAss 27
currentOcc - 124259
ID'S MATCH
809 - Realmsmen III
leadAss - 28
currentOcc - 124258
ID's MATCH
810 - Realmsmen IV
leadAss - 29
currentOcc - 124257
ID's MATCH
811 - Realmsmen V
leadAss - 30
currentOcc - 124256
ID'S Match
812 - Realmsmen VI
leadAss - 31
currentOcc - 124255
ID'S MATCH
813 - Realmsmen VII
leadAss - 32
currentOcc - 124232
ID'S MATCH
814 - Questors
leadAss - 33
currentOcc - 118242
ID'S MATCH
.
IMPORTANT: HERE IS THE NEW SAVE AFTER THE END OF MY TURN.I IMPLORE you all to go ahead and do some extensive testing, just because I had no crashes after this fix doesn't mean it wasn't a fluke or only a temporary patch.