Google has updated the help document on how to verify your business to say "we may require you to verify by more than one method." So if you verify using one method, Google might decide it needs you to verify again but using a different method.
Here is a screenshot of the help document:
Stefan Somborac who spotted this said on Twitter that maybe this will lead to "a stricter verification process" and thus possibly "reduce fake locations on Google Maps." Maybe?
The current verification methods include phone or text, email, video recording, live video call or postcard.
Forum discussion at Twitter.