For 26.3 (and probably going forward, unfortunately), you cannot have unknown data in a data pack or else Minecraft will refuse to reload any loaded packs. Allowing unknown data was apparently a bug fixed in 26.3-snapshot-5. As such, you will have to remove anything in the data folder that you don't have installed. Here's a list of the folder names and what the mod names are for reference:

biomesoplenty				Biomes O' Plenty
ecologics					Ecologics