Quickset is extremely picky, as soon as you do anything that is out of its (narrow) pre-determined path, it will botch your configuration, hence the usual recommendation is to not use it at all.
The default configuration (after a reset) is (should be) already a good base to build upon WITHOUT recurring to Quickset, which in any case can ONLY be run ONCE right after a reset.
This is Rule #4 (you might find of use also the other ones):
The twelve Rules of Mikrotik Club
This said, some devices may "prefer" to use automatically some frequencies/channels at the top of the 5 GHz range and a lot of clients simply cannot use them, hence it is usually recommended to set manually one (or a few) 5 GHz frequencies.
This may also depend on the RouterOS version you are running and on the drivers (wireless or wifi-qcom-ac) you are using.
Please post these details, then, starting from the default configuration it will be possible to give you more accurate advice.