RUT906 firmware 7.7.1 mqtt to modbus issue

while working on the issue cited here, I tried different firmware:
-7.5.4 : MQTT modbus gateway works ok
-7.6 : Same behavior, ok on this
-7.7.1(latest) : MQTT modbus gateway does not work anymore. I receive “invalid argument” error with the same request. Is there a change on this?

here is the request:

1 2 0001 2 70 15 2003 1 1

with tag 2, 0001 as my device(RS485), 2 seconds delay, 70 as device address, 15 for writing multiple, 2003 for coil address.

I tried directly on the webUI to control the modbus via “modbus serial client” page and the request works fine.

Thanks for your reply