No internet connection after switching between ISP and Mikrotik AP

Today I implemented a Mikrotik AP in my home network. I thought everything works fine so far, unfortunately there is a problem which is very annoying.

If I am connected to my ISP AP/router, then I get the IP from this. As soon as I go to the other room where the Mikrotik AP was installed, the WLAN is switched, but there is no connection to the Internet. I only get an internet connection after about 5-10 minutes. However, switching from Mikrotik AP to ISP AP works fine.

ISP AP: 10.0.0.138
Mikrotik AP: 10.0.0.139

Hope sombody can help me. Thanks in advance!