403 forbidden errors sporadically

Just noticed today that some of my sites are getting 403 errors when I access them from my home cable modem, but not when I access them via my mobile phone. And some directories give 403 errors but other don’t.

For instance:

From my cable modem connection I can access:
https://stepmomgifts.com/product-category/pillows/
But I get a 403 trying to access:
https://stepmomgifts.com/product-category/books/
OR: https://stepmomgifts.com/wp-admin/

All of these URLs are accessible just fine via my mobile phone’s cellular connection. But if I connect to my cable modem connection via wi-fi on the phone, then I get the 403 errors.

Any ideas why a 403 error would be only on my cable modem connection, and only on certain directories? I rebooted the cable modem and router to no avail. No other browsing seems to be affected.