The namespace still has 380,000 domains.

.App registrations fell on the one year anniversary, but the namespace still has about 380,000 domains. Image from nTLDstats.
Google’s .app domain name entered general availability on May 8, 2018. It immediately took off with 100,000 domains registered almost immediately and 180,000 domains under management within a couple of days.
There are now 180,000 .app domain names and rising!
— Ben McIlwain (@CydeWeys) May 10, 2018
These early registrations came up for renewal in May this year. The first anniversary of a domain launch is often called “the junk drop”. People who got a bit too excited at launch drop their marginal domains.
In the case of .app, it took a while to see the impact of this. It takes up to 80 days for .app domains to work through the deletion process: up to 45 days of autorenew grace, then a 30 day redemption grace period followed by 5 days of pending delete.
The .app namespace continued to grow up until July 13, according to nTLDStats. Then the early domains started to drop and the zone shrunk, but it hasn’t been too bad.
nTLDstats shows that the namespace peaked at 446,730 domains on July 12. It is now 381,195. (There are fewer domains in the zone file, but nTLD stats estimates domains that don’t have nameservers.)
Based on these data, the namespace has lost over 65,000 domains. New domains have been registered during this period that offset some of the losses.
Ben McIlwain of Google Registry told Domain Name Wire:
We are happy with .app’s strong renewal rates. This validates our belief that customers are interested in new TLDs, and in the case of .app especially as meaningful, functional and more secure gateways to the internet. We look forward to seeing more developers building on .app.