The personal workbook opens for new files but not existing files.

Things I have tried:
If I try to record a macro on the personal workbook in an existing file I get two errors:
"Personal Macro Workbook in the startup folder must stay open for recording"
"Unable to record."

the personal workbook is not disabled in the trust center.
trusted documents and locations are not disabled

if I put in the location of the XLSTART folder in the "at startup, open all files in:" it works only until I close Excel: it then goes back to being blank.

I have literally no idea what to try next.