I can’t identify any mistakes… all looks good… (calimero even reports that you get confirmations)
try to remove the status GA (from the item config in OH2) to see if the command succeeds
similar situation here:
Ps: Are you 100% sure that this GA (1/0/12) is the correct one for Up/Down?
(edit) Ps2: I see that OH2 is using PA 1.1.28 (cEMI L-Data.req from 1.1.128 to 1/0/12) while this is the PA of the knxd process and the clients should start from 1.1.129. Maybe try to define the PA (1.1.129) in your knx.cfg file?
(edit) Ps3: which version of knxd are you running? I saw that this internal error: send_more is not set has been fixed in the latest release. Maybe try the newest version of knxd?