Remote access via ReadyCloud Desktop sometimes works, sometimes doesn't

While ReadyCloud was a fine quick solution for folks who suddenly had to work from home due to COVID, I don't recommend it as a permanent solution for a business.  In fact, I don't use it at all for even personal stuff.  The reasons are many:  Your situation doesn't seem uncommon, based on posts here, especially associated with updates to any Apple OS.  It relies on the Netgear server being up and reachable.  It's limited to Netgear and whatever they decide to support.

A better VPN is what I recommend.  That won't have any sync capability built in, if you even use that, but there are plenty of sync solutions that work over a VPN.

I personally use ZeroTier as my VPN.  In addition to everything I can do with ReadyCloud, my main and remote NAS can do backups over it, I use the same login credentials whether local or remote, and I can put it on pretty much any Linux, Windows, Mac, Andriod, or IOS system I want, including another brand of NAS.  Zerotier does also rely on an external server as the initial "operator", but it has proven to be reliable.

OpenVPN is another option, especially if it's built in to your router.  It does not rely on any server not within your own control and it can allow you do do the same stuff I do via ZeroTier.