APM Session deleted when following link Webtop Link to Application URI

From what I see you are matching the issue in and this was version 12.1.2, so it seems an expected thing:

https://devcentral.f5.com/s/question/0D51T00006i7hk3/domain-cookie-sso

Can you also check if you have set the cookie with a persistant flag as this will not work for the webtop "Persistent: Session cookie persistence functions only on BIG-IP LTM and APM deployments. For BIG-IP APM deployments with connectivity resources (such as Network Access, Portal Access, etc.), you cannot set BIG-IP APM cookies as Persistent. This is by design, as session cookie persistence can present a security risk. For some deployments of the BIG-IP APM system, as with Microsoft SharePoint, cookie persistence may be required. When you select cookie persistence, persistence is hard coded at 60 seconds."

https://support.f5.com/csp/article/K15387

Also you use domain cookie because you want an SSO, so when the user logs into the APM to also be authenticated to the backend applications without again entering credentials?

Did you test without SSO and domain cookie just with Global profile scope if the session is deleted when accessing the webtop after first going to the application as maybe the SSO is the reason and maybe the webtop SSO does not work corectly?