Hi!
Regarding the “slave1”, it sounds like you are suffering from issue #5084 which was due to larger issue in openHAB itself.
It seems that a suggestion is to have a “pid marker” in the config file, as described here. I am not sure of the exact syntax though…
Clearing the cache might help as well. Whole cache can be cleared like this, or just the modbus binding cache: config:del org.openhab.modbus.
Regarding your write errors: do you see any ERROR lines in the logs?
Best,
Sami