Zrevnur: But be aware that there are many bad bugs and other issues which cant be fixed by modding the .xml files.
Karavox: Very bad if so. But what about those of them that could be mended with XML-editing? Do you have some info on this matter? I'd be grateful to you for sharing.
Unfixable bugs: Some of the worst: End turn hang, tactical combat stuck, movement bugs, movement prediction bugs, many update bugs, never-load-unless-directly-after-game-start bug + dont-use-Ctrl-N, autosaves may contain a game state which couldnt happen normally
There are also many questionable (IMO very bad) design decisions which cant be fixed like the way (even unintentional) army stacking kills movement and overflow production being lost.
Then there are some things which I dont even know if its a bug or an intentional feature like combat sometimes using unpredictably high amount of movement points.
And for "serious" players the UI has also severe issues like the way unit cycling works - or rather misworks.
XML bugs: As my playing is based on Xtra Deconstruct mod I dont remember seeing many .xml bugs and the ones I have seen may have been introduced by the mod. [url=See https://www.gog.com/forum/fallen_enchantress/lh_20_xtradeconstruct_legacy_of_magic_mod]See https://www.gog.com/forum/fallen_enchantress/lh_20_xtradeconstruct_legacy_of_magic_mod[/url]
Far as I know though the Xtra Deconstruct mod fixes a lot of .xml bugs in the base game. There are also some remnants of this in its user guide. Like:
58. Why are islands sometimes spawning on the outskirt of the map?
XI_WorldMonuments.xml
XY_Miscellaneous.xml
Some of the fixes in Xtra Deconstruct may have been fixed in recent official patches though.
Anyway about .xml bugs the one most knowledgable non-Stardock is probably the author of the Xtra Deconstruct mod.
Edit added more unfixable bugs