WAF Slow https Access to internal DevOps Server 2020

Hi,

i used to have pubished TFS 2015 with different XG Releases (17.0,17.5,18.0 and 18.5).
Users connected to the Webinterface of TFS through a Public URL and XG had a simple rule with Form bases authenticationa against the TFS 2015.

Last week i changed the TFS 2015 and upgraded to DevOps 2020.

Now the DevOp Server is slow and access with htts is realy getting slow.
Local Access inside the DevOps Server Network is very fast.

Firewall HW used is a SG 210 Rev .2 with XG 18.0.5 / 18.5.1

Has anyone an idea why DevOps WAF is gettings slow?

Thanks

Jürgen