Combining PDF's is corrupting the resulting PDF

I have a lot of PDF's that I combine and this is the first time I have encountered this, a small bit of history, these PDF's were created a few months ago in Adobe Acrobat Standard, they have worked flawlessly, now I am getting really weird things going on, even if I combine just a single file the same happens so it's nothing to do with same field names in different documents. Getting the field list up and sorting alphabetically there are no duplicates so its not that.

Specifically what is happening when a combine happens a number of the text boxes get converted into fields in the document, its the same textboxes each time. Clicking on properties the fields are dead there are no properties.

The new document works ok until you save it, so the intially created combined document is ok until its saved.

It does not matter which combine file size options.

It gets a bit weirder, go to the original PDF document, copy one of the text boxes that does not corrupt, paste it anywhere in the PDF, save the PDF document, do a combine of the single document, save it, then the corrupted fields change.

I am running the latest version of Adobe Acrobat Standard on MacOS (latest version).

Here is a screenshot of what it looks like after a combine and save.