I'm having issue connecting to BT IP addresses that I use for work. If I try with the DSL line connected traceroute fails, if I disconnect the DSL line and use 4G BT failover then it works correctly. Testing from other non-BT sites also works.
I have the same problem which you can see at
The BT support says access to static IP is the owner problem and refuse to look into problem.
Moreover, I had some IPs which were blocked even by 4G failover.