Console not showing right log

I want to troubleshoot some modbus communications.
when I use this in the console:
log:set DEBUG org.openhab.binding.modbus
There is a lot of [INFO], however nothing from the modbus binding.
The modbus communication works, as I can read some registers from the device.
How to get the debug info for the modbus binding?

Check the output of log:get org.openhab.binding.modbus.

Then try reading the openhab.log file in a text editor. You should at least see this, if the binding is running:

Modbus binding has been started.

Found it, for a reason I cannot explain, 2 of the 3 used bindings were uninstalled.
Modbus and http binding wasn’t installed, no problem with the Onkyo binding.
Re-installed both bindings, everything is fine.
One question, the values in shown the sitemap from the modbus device, were the last values readed.
Is there a way to show blancs or zero if the commincation is failing?

When a value switches to UNDEF it’ll show as a hyphen -.
Not sure how modbus handles communication failures.