First off all my english isn’t perfect so i try my best here.
We have a unifi site with 10 ap’s perfect coverage for all devices, only our voip wifi devices are struggeling very hard.
Outbound talk is stuttering and bad quality but not always.
incoming traffic to the phones is always perfect.
Thanks for your thoughts on it every answer of question will help me alot.
below a screenshot of a connection of the device during night time: