V 1.98, Eriador battle playtest 1 (as for Aringtoit's Eriador/Barrow Downs in-battle crash report).
Get mission Barrow Downs in the 1st end_turn.
I take Gandalf and his 3 allied archer units (Ithilien Ranger, Elven Sentinel and Bandoras Hobbit) plus Halbarad (Grey Company bg) from Staddle to engage the close-by Bree Bandits band, formerly discovered via spy. I attack. Battle runs issue-free, everything normal, all units were engaged.
Afterwards i take (in the meantime partly armour upgraded) units from Bree: Woodland Archer, Lumbermen, Greenway Guards plus Bree Archer from Staddle and Gandalf and Halbarad to engage vs. Barrow-Downs. I siege them until they sally out which is the 2nd turn after siege. Battle runs issue-free, everything normal, all units were engaged.
Getting the successful-mission message and the unit reward into Bree, which is one Greenway Guard unit.
No battle issues in sight.
Aringtoit, if your in-battle crash remains, please list exactly your units. I take every crash-report serious (and will help where i can, ie. possibly a file change on your side is the culprit), and just in case, please use v1.98, not v1.97 incl. temp fix (although that should work as well). And there is no need to edit the Dismounted Dunedain Knight unit, it's done with v1.98.
Edit
By chance, did the Barrow Downs Orc Looter garrison get reinforcements from the nearby (hidden) Orc Looters? Perhaps you suffered from the very seldom reinforcement-battle-bug?Going to try to fight that battle again and see if it crashes again. I'll let you know. 1st time I've gotten an in battle crash with your mod without there being a relieving army involved. It's an "unspecified error" crash btw. I'll let you know how it turns out.