Apple TV dropping Screen Mirroring

Dropping will usually come down to an issue with the connection, which can happen at any time. Worth noting that mirroring is more intensive than standard airplay as it is sending out a device's display in real time so it needs a much more stable connection.

Make sure no other activity is occurring on the network (other streaming, web use, network backups etc)

If on wifi try Apple TV on ethernet

To see a current status of the network get a report using istumbler or similar. Look for signal strength, noise, nearby networks

That doesn't rule out a network issue. There have been select users over the years who have had a similar experience and because it happened to occur after an update they assumed that it was the cause. Of those who went ahead with an investigation it has in fact been a connection issue and rectified. Ultimately, it's best not make an assumption and look into it more.

Again, another device working does not rule out a network issue. There are select threads from users who happened to experience the issue and have linked it with the update. The same occurred after the previous version was released, and others before it. If it were an issue directly with the update then there would be a consistently high rate or reports, it would be easy to replicate by regular testers, and this thread would have also received a multitude of responses by now.

If you wanted to adequately rule out the network then you would have had to follow what was advised above. However, it seems that you want to continue on with an assumption so there is no way to move forward based on that premise. I will bow out of this discussion and leave you to do as you wish.

Another device working does not rule out the network

Same issue for me. Started after big update. Apple TV gets more unstable.

Don’t know how to get a more stable apple tv ...