"Default title" error on product imports shows in store listing

[shopfy-2020]

As if Shopify is not already covered in enough tech issues and limitations, here's a new one I never had problems with before:

1. Importing files: After the review app stopped working and I had to find another app to resolve the issue with importing previous reviews, the app of course had their own csv structure. Based on that, I had to rename the file handlers for all products. This resulted in Shopify importing duplicates of everything.... So, now I had to delete all products and re-import them. This lead to another problem: Shopify could now not find any of the images for the products and could not import any them.... I now have to manually add all images for 800 products....

2. "Default title" error: Importing products a new headache has appeared. On every product listing the store view  now shows the variants and an ugly 'default title' option as well. This never used to happen with previous product imports.

How do I remove or correct the "Default title" error in every product listing in BULK without having to manually piddle with this?