Another member of this forum posted recently of "zeros" for several clients during a period in March. I was looking for that thread because I too have experienced this "phenomenon". I couldn't find it (yet) but in the meantime I found your post here.
I have had several clients with very robust listings suddenly "zero" out for a day or two. I first noticed it in August, and it's occurred sporadically since then.
Today I noticed something interesting. A client with a very strong local presence has seen a steady decline in Search and Maps Views this past week, according to GMB Insights. This same client had two "zero days" on 3/2 and 3/3.
It didn't make any sense then and still doesn't. You don't go from 3,000 views one day to zero the next. Must be a reporting error. It happens.
In trying to determine whether I have a problem with their recently declining Views, according to GMB Insights, I looked at the Quarterly results. The March "zero days" are gone.
I'm hoping that the recent decline is another anomaly. Client says business has been reasonably good this past week.
I use Bright Local for a lot of things. One being their Rank Checker. I was curious whether their reported rankings have taken a hit lately. When I logged on I was greeted with a pop-up from Myles stating that some of their reporting tools were experiencing problems, they were working feverishly on resolving it, sorry for inconvenience...
I wonder if all of this is related.
My advice to you. Have a nice glass of wine and come back tomorrow. Things change rapidly around here.
But curious on what others in this forum have found with "Zero Days", ranking reports and Insights validity,.