GMBapi reports on deleted reviews for all of our customers, so you can keep an eye on this and know exactly what has been deleted. We are seeing the same thing, review deletion is rising, and it goes in waves, different per client, sector and country. We always advise to request the review back, but we are seeing the success percentage of that effort slowly dropping over time. So consider whether it is worth it on a location by location basis, thinking about factors such as "local competitivenes", "recency and count of reviews", "ease of getting new reviews for that location" - and then make a judgement on whetehr you invest the time to attempt to get the reviews re-instated.