After the latest updates I'm seeing problems on both my (Note 9) and my partners (S9Plus) phones that did not occur prior to the updates.
1) WiFi connectivity
At home we have a Netgear Orbi mesh network. Previously moving around the house (switching between the satellites) there was never an issue with connectivity on WiFi. Post update apps / browsers will report no network as we move around. The work around for this is to turn off the WiFi and then turn it back on.
As the Note 9 and S9 Plus received the updates some weeks apart and the issue only occurs post update, this points to the update causing the issue, not the Orbi firmware.
2) Message threads are slow to / do not update in the built in app
If I have a message thread open in the built in app and someone sends me a message, there is either a considerable delay in the new message being displayed or the conversation simply never updates.
I will receive notification of a new message arriving on the notification feed, and it will show up on connected devices capable of displaying messages (smart watch and PC) , but the app will not update the conversation
The work around for this is to back out to the list of call conversations where the latest message will be displayed and then reenter the conversation.
3) Random apps / screens displayed as I switch apps / unlock phone.
The screen will show flashes of random apps as I unlock the phone / switch to another app. This did not happen before the update - I am using the Microsoft Launcher rather than the default one on the phones, but this is still a change in behaviour post update.
We have the Orbi setup as well. Other devices working great like usual, our Note 9's however are not acting right on wifi now. I can run a speedtest on the phone and it shows over 200 Mb/s but some apps and email will act like I have no connection. Sometimes shutting the wifi off and on again fixes it, othertimes it does not. We have 2 Note 9's and they are both doing the same thing after the updates. All the streaming devices we have work fine, no issues so its something with the update. (Orbi hasnt had a recent update either and is up to date).
We do not seem to be having the app switching or displaying issue you seem to be having so that might be the update messing with the loader you are using.
I have noticed issues with messages, and I have tried both the samsung messenger app thats built in and the Verizon one. I'll get an audible notification as well as the led light, but when i go to see what it is, its gone, and I have no updated messages on anything. I have had a few people tell me they texted me something and I have not recieved it. Not really an ideal issue to have during this time.