Streaming locally over WiFi and buffering

[DeanoVIP]

I know I shouldn't use WiFi but I don't have a choice currently.

My setup is as followed:

Ground Floor:
Router (WiFi 6) and TV - Roku Box w/ Jellyfin app

Middle floor:
Repeater Mesh setup (WiFi 5)
 TV - Roku Box w/ Jellyfin app

Top Floor
Jellyfin Server with TP link WiFi adapter AC1300 WiFi 5
TV with Chromecast /w Jellyfin app.

Now from a internet perspective I get 500 down and 70 up and on the top floor I get the same over WiFi from the repeater from my laptop.  The server gets around 300 down and 60 up just to give and idea of how well the coverage is.

I find when streaming to the top and middle floor it's fine, however the ground floor down things play flawlessly others buffer loads.  For example play a show that's h264 and the Bitrate is showing as 10Mbps and buffers like mad.

What can I do to diagnose this issue? Or improve it somewhat but remaining on WiFi.  I find sometimes playing h264 or 265 fine and even have 10bit.  The local lan is not busy just this.