Crash on Factorio Load, message:

127.492 Error ModManager.cpp:1764: Error in assignID: recipe with name 'foliax-bronze-bar' does not exist.
Source: foliax-bars-productivity (technology).

Edit:
I haven't got BZTin installed, and in your prototypes/mod-compat.lua, you guard the addition of foliax-bronze-bar in L1017 against the mod being present in the first place in L978; however, could the problem be that in L1100 you add an effect to foliax-bronze-bar when the tech foliax-bars-productivity is researched, even though there's no recipe foliax-bronze-bar without BZTin? Should you maybe move the add_tech_effect in L1100 into the if mods["bztin"] block in L978? As you do e.g. for foliax-tech-tin in L991?

Or, as you do with add_to_recipe in L67, maybe only add the effect in add_tech_effect if the effect's recipe exists (IF it's an effect targeting a recipe)?

Edit 2:
Just to confirm, if I delete L1100-1105 (since I don't need those anyway since I don't use BZTin), Factorio starts without issues.

That was a dumb mistake on my end, thanks for investigating and providing the solution. Moved the bars productivity addition of bronze bar up to the bronze section. Released a new version, thanks again for your feedback!