Dynamic tunnels on Mikrotik, how to get rid of?

Question

VPN

There is a central gateway to which tunnels (L2TP, PPTP) are raised by other gateways, also Mikrotik.
Despite the fact that static interfaces (Server Binding) are registered on the central one in PPP, to which the corresponding Secrets are bound, and to which static routes are registered, sometimes dynamic interfaces are created when connected. Naturally, the static route "breaks" in this case.
It helps to remove the dynamically created interface, then the connection rises through the server binding configured for it.
Why is this happening at all, where to look?