the development of Codesys support has been dropped altogether. The Codesys can be still used on Neuron via ModbusTCP. The Unipi 1.1 doesn't have IOs accessible via ModbusTCP, only scattered over I2C, GPIO and so on - nothing easily configurable.
@lefrank01 thank you for sharing your tips. I have also had this reported once or twice and on each occasion starting from a clean install of Raspbian, installing CODESYS for Raspberry Pi and then running the script that ships with CODESYS for UniPi has resolved users problems.