I have two EAP773 where MLO is working perfectly - I recently added a EAP770 and copied the same settings to it but the clients will not connect to it with MLO. 

If you reboot the AP you will see the client connect to it with MLO with the 5ghz network green and the 6ghz network gray but after a couple of minutes the 6ghz will drop, the MLO designation will disappear and the client will be connected via the 5ghz radio only.   

I created a 6ghz only network and that still works during this time so the 6ghz radio doesn't die its just the MLO is not functioning properly forcing clients to 5ghz only.  

I tried with the Iphone 16pro, 17pro and Samsung Galaxy S24 - all show the same behavior on the EAP770 while working correctly on the EAP773's.