losing access after VPN establishing

Hello

I have a Mikrotik VPS version 6.40.3 which PPP > SSTP VPN is configured and I call it Mik A here to explain my solution and issue on it and there is another Mikrotik is called MikB.

Solution :
MikB is set with SSTP client that establishes SSTP VPN to MikA . its working fine and all traffic goes through the tunnel easy.

Problem:

After establishing the VPN connection because of changing IP address to MikA NAT IP I lose access to MikB from outside, and this issue effects on all my des-nat configuration on MikB. is there any way I could to fix this issue.

Best Regards
Yashar