Redirect to home page at checkout

Hi,
We’re having a few instances of users being redirected to the home page at checkout. This happened previously and this seemed to fix it.

define('GEODIR_USE_PHP_SESSIONS', false);

But now we’re seeing this issue again, on occasion.
I’ve tested myself successfully for these configurations:
Mac – Safari, Chrome and Firefox
Windows 10 (via Parallels) – Edge and Chrome

I’ve checked the user agents for the past few users who were redirected and they were all using Windows 10 & Chrome. Not sure if this is the cause but not convinced that it’s a coincidence either.

Any guidance is appreciated…
-larry