Hi, it's me again! I'm having this error. I think it's related to the LTN mod, because the error didn't appear before installing the train station. By the way, is it possible to disable the mod for a specific surface? Specifically, for the designer's sandbox.

Error while running event quality-control::on_nth_tick(1)
LuaEntity API call when LuaEntity was invalid.
stack traceback:
[C]: in function 'index'
__quality-control/scripts/core.lua:399: in function 'attempt_upgrade_normal'
quality-control/scripts/core.lua:503: in function 'process_upgrade_attempts'
quality-control/scripts/core.lua:676: in function <quality-control/scripts/core.lua:617>

https://drive.google.com/drive/folders/1xgRuENiWxJUJ6lfEq6sYYi9XNq4w0DUk?hl=ru

Oh, nice find! I'll take a look and figure out which entity is causing the issue. Thanks for finding and reporting.

It should absolutely be possible to disable for certain surfaces. I'll look into it - I assume the designer's sandbox surface is related to the in-game editor?

Would like to add it has been happening to me too, unsure what mod is causing it, possibly its my own mod but im unsure if it would as i assume its compatible with any roboport prototype.

@Smougtea - I think the error was actually coming from interacting with the blueprint sandbox mod. So I'm glad you asked about it!! What I think was happening was Quality Control tried to upgrade an entity in a sandbox, blueprint sandboxes did something, then quality control didn't handle what happened next.

Anyway, I think it's fixed with version 1.6.1 - I couldn't get the error to occur again in the save file you shared. Please let me know if you run into it again?

@Vadeblad - are you also using the blueprint sandbox mod? If not, would you be ok sharing a savegame from just before a crash? I can take a look and see what's going on, maybe there is a compatibility issue between our mods.