Autofill Other Forms not working

I complete forms on a particular website regularly. I used to be prompted (I cannot remember when this stopped, but it was after updating Safari - now 15.6) with previous entries in each field via a dropdown box (these were not generated by the site).

For eg. If in a particular field I'd previously (on different occasions) entered: 1234, 1235, 1236 & 1237 then as soon as I started typing 1 in that field a dropdown box would open with all these as suggestions to choose from. This would include complete sentences. This no longer occurs.

I've spent much time searching for solutions after trying the obvious: turning off autofill/other forms, restarting Safari and turning it back on again to no avail.

I have deleted ~library/Safari/FormValues.

Is there a way to force information entered on a web page form to be saved?

If anyone can help me, it will save me an incredible amount of time over the rest of my life?

Autofill for this same form works just fine if I use Chrome...