[0.13.8] Error migrating 0.12 save: No covariant prototype

[Nevermind]

I ran this save on .12.35 with bob's library and all of the 5dim modules (among a few other mods like RSO, Warehousing, YARM, Fat Controller, etc). I am quite attached to this savegame, but I do want to migrate to .13
I have deleted all of my .12.35 mods and installed bob's library and all of the 5dim modules from the .13 mod interface. They are up-to-date as of 15 minutes ago.

The exact message I get is:

Notice

No covariant prototype to load 5d-mk2-transport-
belt-to-ground-30, that was saved as type
transport-belt-to-ground, but is now
underground-belt

Is this an error in the mod code or is this something that I will have to edit my save to fix? If I have to edit my save, what would be the best way to do so? I have unzipped my save and opened level.dat in a text editor, but judging by the number of non-ascii characters, I don't think that is the correct method.

Would it be easier to revert to .12.35 and remove those 30-length underground belts in-game?

[kinnom]

seems to be a problem in the migration files in 5dim's transport
can you upload the log and the save?

[Nevermind]

Thanks for your help and sorry for the delay in replying. I am now on version 0.13.11 (with up-to-date mods via https://mods.factorio.com)

Loading is still broken on this save.

[Nexela]

make a backup and load your save in .12.35 without that 5d mod, save it then try and load into .13

You might lose some stuff depending on how much you used but the world might load

[kinnom]

strage, the log simply stops in the midst of the migrations