Does failover from active device to standby device cause the active applications running on F5 disconnect ?

You mean reset the current connections? That depends on whether you have a 2 node cluster with connection mirroring on it (Or are using a VS with loose-init) or not...

If your VS's are using mirrored connections, then they should be valid on the second device when it goes active. If you're using standard VS's with no mirroring (not configured, or > 2 nodes in the DSC) then they'll get reset when you try to push traffic through them because they won't be in the new active devices connection table

H