Low speed when connecting point-to-multipoint on Mikrotik?

Question

WiFi

Good afternoon.
There is a small radio network. PPPoE from the provider raises Mikrotik hEx RB750 Gr3, it has a PPPoE server configured for 10 users at 10 Mbps.
MikroTik BaseBox 5 RB912UAG-5HPnD is installed as a base. Subscribers have MikroTik Disc lite 5 installed.
When connecting more than 5 subscribers, the total speed that BaseBox can give drops to 20-30 Mbps. If you connect directly from the router with a cable, then all the rules, it gives out 100.
Maybe someone came across? Tell me where to dig? Is this the BaseBox limit or is there a problem somewhere in the settings?

Answer 1

Thank you all for your help, changing the frequency to a less noisy one solved the problem!

Answer 2

maybe more. but not for 10 points