I have an APM IdP bound to an external SP. When a user logs out off the SP Application, SLO kicks in and the user is directed to https://myidp.com/saml/idp/profile/post/sls. The APM session is removed but this page results in an error connection reset and the user is left on the "Thi Sit can't be reached) page
You may check the apm logs as there could be bugs as this one https://cdn.f5.com/product/bugtracker/ID766577.html and F5 bug tracker will help you search for them. Who initiates the SLO the IdP or SP and is the F5 device the IdP in your case?
Also test with changing between POST and Redirect binding SLO URL as the different browsers and their versions may react differently to the SLO URL, so see the article https://support.f5.com/csp/article/K67310544 and if needed use HTTPWatch or Fiddler to see what HTTP SAML messages the client sees and then decode the SAML info by following https://support.f5.com/csp/article/K51854802 .
