Screen Mirroring hickups

Using screen mirroring works okay, but after about 15-20 minutes the service stutters - videos hanging for a second or sound issues or both.
Older (5 years) phone using same apps, same wifi and same tv works perfectly, so this is an fp5 issue.
No big deal, as screen mirroring is not my main task for this phone, but a performance problem all the same.

Anyone else recognized this?
Any solution (maybe a setting i do not know of cleaning the memory)?

I want to mirror my FB5 on my Kenwood car radio.
How can I achiev this?
Thanks for help.