403 Forbidden when trying to update string translations

I have come across what seems to be a bug which I can consistently reproduce as follows:

On my’Strings translations’ page (https://www.liz-cox.org/wp-admin/admin.php?page=mlang_strings) when I search translations’ with the string of ‘by’ 9 pages are returned from my English to Spanish database.

The string that I want to update is on page 6. When I amend the Spanish ‘by’ to read ‘por’ and click on ‘save changes’ I get the ‘403 Forbidden’ message with detail of ‘www.liz-cox.org/wp-admin/admin.php?page=mlang_strings&s=by&group=-1&paged=5&noheader=true (port 443)’

I have found that I can update strings on pages 1, 2, 3, 4, 7 & 9 without problems, but any string updates on pages 5, 6 & 8, for this particular search, all error with a 403!

I have found that by performing a descending sort on the ‘String’ column I can get the ‘by’ string that I want to amend onto page 1 of the 9 page search and so am able to update it.

So I have a work around, but thought you would like to be aware of what feels like a bizarre bug

The page I need help with: [log in to see the link]