The v8 firmware is fine, latest(or last) chip is 8.140, the firmware must match on IP adapters, so if one is v1.0 and one is v1.1 they will not talk. There is absolutely no way to downgrade firmware on these adapters you must upgrade all to v1.1 if they are different. Annoying as I have seen situations where 10+ v1.0 adapters have to be upgraded just to work with one new IP Lan module.
If firmware is all v1.1 then I would also test the adapters with software below from one modules location to the other they need to be within the threshold defined by Tecom of 40ms.
Also these adapters are shipped with CFG link on & when powercycled with this link on it defaults the adapter, so if they are new and were configured with the link on they may have lost programming.
Firmware update:
Network Tester:
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