Dear Ofnuts 
I was going to put up a bug report, This using BIMP as the batch process. A 3 layer image, exported as a multi-layer tiff with all other options OFF. The same image / settings but with different compression formats (just in case)
I can guess the response from the devs. External plugin, contact the maintainer for a fix.
Edit: A few more tests and it does seem to be a Gimp 2.10.30 issue (certainly not a 13 year old bug)
I can convert (tiff to flattened tiff or tiff to jpeg) those files using Gimp 2.10.22 using BIMP and get no errors.
FWIW I posted a bug report : https://gitlab.gnome.org/GNOME/gimp/-/issues/7852
--- off topic, but I think you have a comment in the bug thread. From the dev notes update ---
Stroking a path with source tools (Clone, Heal…) is now possible
when the tool is active and a source was selected.
Technically it's more of a bug fix because the GUI existed as though
it was meant to work, but since the report has existed for more than
13 years and I'm not sure it has ever worked
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I was going to put up a bug report, This using BIMP as the batch process. A 3 layer image, exported as a multi-layer tiff with all other options OFF. The same image / settings but with different compression formats (just in case)I can guess the response from the devs. External plugin, contact the maintainer for a fix.
Edit: A few more tests and it does seem to be a Gimp 2.10.30 issue (certainly not a 13 year old bug)
I can convert (tiff to flattened tiff or tiff to jpeg) those files using Gimp 2.10.22 using BIMP and get no errors.
FWIW I posted a bug report : https://gitlab.gnome.org/GNOME/gimp/-/issues/7852
--- off topic, but I think you have a comment in the bug thread. From the dev notes update ---
Stroking a path with source tools (Clone, Heal…) is now possible
when the tool is active and a source was selected.
Technically it's more of a bug fix because the GUI existed as though
it was meant to work, but since the report has existed for more than
13 years and I'm not sure it has ever worked
-----