I have a site with a checkout page that has always worked beautifully.
Recently, any customer that uses autofill to fill out his info, gets his email address dumped into the company field.
There are no changes that we did that could affect that.
What other tools can I use to get to the bottom of this?
The OP's problem may have been solved (or may have come back again in recent updates!) but as of early 2019, you can diagnose some of these problems by setting the show-autofill-type-predictions
flag in chrome://flags
, restarting Chrome, then looking at the title (tooltip text) for the input in question. It will tell you what information is being used to guess the "type" of field, and what kind of saved data should be used to populate it.