Hello,
I use a GROOVEA52HPN as access point and GROOVE52HPN as station (Wireless Protocoll is 802.11; Frequency 5745 MHz).
If I configure the system with 20 MHz everythink is fine, but with 5 MHz and 10 MHz channel width no connection is possible.

What is the problem?

Thanks.

Please upgrade RouterOS to v6.25 and check again.