Hi Adam.
Thank you for your response.
The Ajax was already disabled but, after a lot of trial and error, we think it may have been an error linked to the akismet spam filter (in Security) as after disabling this the problem seems to have stopped.
It could be this in conjunction with the custom code we implemented.
I’ll be in contact again if we notice the error again.
Kind Regards
Thank you so much @wpmudevsupport15 and @wpmudev-support8 for the swift response!
This code helped a lot!
We had to tweak it slightly as when we tested it, the output was incremented again (so, for example, if the form code was saved internally as number 10, the user received a message saying the code is 11…).
So I changed the else statement to
$incremental = $incremental + 0;
It seems to now be working exactly as we wanted.
Thank you again!