EoE communication SIS and S/IP cannot be established (CtrlX Engineering)

Dear community,

I have a setup with a number of CtrlX drives (V-05RS) connected in an EtherCAT bus with an EtherCAT Master running on a Beckhoff IPC (TwinCAT/BSD) based on CoE (CiA402).

The hardware connections are as follows: Windows PC (CtrlX Engineering) <=> Engineering port TwinCAT/BSD PC <=> EtherCAT Master port TwinCAT/BSD PC <--> CtlrX Drives 1..X.

The EtherCAT master has IP address 192.168.100.99/24. The CtrlX Drives have unique IP addresses in the same subnet (192.168.100.XXX/24) each with the default gateway set to 192.168.100.99 (the EtherCAT Master). The engineering port on the TwinCAT/BSD PC (192.168.2.50) and the Windows Ethernet adapter (192.168.2.10) are both on the IP subnet 192.168.2.XXX/24. Furthermore, EoE is enabled in the EtherCAT Master with the EtherCAT Mailbox Gateway set to 192.168.100.254 and IP forwarding on the TwinCAT/BSD PC is enabled in order to forward IP traffic from the engineering network towards the EtherCAT network. Lastly, a static IP route is defined in Windows using $ route ADD 192.168.100.0 MASK 255.255.255.0 192.168.2.50.

Using this setup, it is possible to successfully ping the drives from the Windows PC. However, when trying to connect with CtrlX Engineering the following message appears: "No parameter communication: This IP address can be contacted using a ping, but the parameter communication (SIS and S/IP) cannot be established." Refer also to attached screenshot.

Can anyone help on achieving successful CtrlX Engineering communication with the described setup? What causes the SIS and S/IP error?

Note that the drives can be controlled successfully via CoE and the EtherCAT bus is in OP state when trying the above.

Thanks!