Mod Version: lootr-fabric-1.20-0.7.33.81

Fabric Loader: 0.16.5

[04:40:59] [Server thread/ERROR]: Loaded a data file with no size: 'lootr/8/85/855e1acd-1093-4320-b83b-161aa78214cc' located in dimension 'ResourceKey[minecraft:dimension / minecraft:overworld]' at 'class_2338{x=1984, y=86, z=204}'. Sizes will be guessed and updated in future. This message will only appear once; if it occurs multiple times for the same location, please report on GitHub.
[04:40:59] [Server thread/INFO]: Resized inventory with key 'lootr/8/85/855e1acd-1093-4320-b83b-161aa78214cc' in dimension 'ResourceKey[minecraft:dimension / minecraft:overworld]' at location 'class_2338{x=1984, y=86, z=204}' from 9 slots to 27 slots.
[04:40:59] [Server thread/INFO]: Resized inventory with key 'lootr/8/85/855e1acd-1093-4320-b83b-161aa78214cc' in dimension 'ResourceKey[minecraft:dimension / minecraft:overworld]' at location 'class_2338{x=1984, y=86, z=204}' from 9 slots to 27 slots.
[04:40:59] [Server thread/INFO]: Resized inventory with key 'lootr/8/85/855e1acd-1093-4320-b83b-161aa78214cc' in dimension 'ResourceKey[minecraft:dimension / minecraft:overworld]' at location 'class_2338{x=1984, y=86, z=204}' from 9 slots to 27 slots.

That should be fine! If this is the initial, first time that you've loaded that version of the mod in that world, it's not an issue.

If you still see the message at a later point, please comment on this issue.