The mod Loaders modernized (0.8.8) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event loaders-modernized::on_built_entity (ID 6)
loaders-modernized/scripts/loaders-modernized.lua:133: attempt to index field 'fast_replace_split' (a nil value)
stack traceback:
loaders-modernized/scripts/loaders-modernized.lua:133: in function 'handler'
core/lualib/event_handler.lua:47: in function <core/lualib/event_handler.lua:45>

Was just placing down a large Gleba blueprint in the 'testing' map editor scenario. No modded tiles, outside miniloaders.
BP string: https://sharetext.io/bb4c0b0a

It sounds like this is probably a user scenario that you saved from the Map Editor? Probably with an earlier version of Loaders Modernized?

The error you're seeing is from data missing in 'Storage' that was added in 0.7.11. After scouring for information on scenarios and migrations it appears that scenarios are not able to properly run on_configuraiton_changed and handle the needed migrations. In fact, devs stated, "Ugh" and "Scenarios are jank, stay away from them if you can 🙃".

It doesn't appear that I'll be able to support appropriate migrations in existing scenarios.