I am using an Ultimaker S5 with the newest firmware (5.1....) and Cura 4.0 freshly installed yesterday.
I have serious problems with the 1. Layer height, because the extruder cloggs during the print which means that to much preasure is in the extruder system. I use nearly standard settings and from my point of view, the first layer is aboslutely to close to the print bed. Due to the autolevel mechanism, there is no chance to influence somehow this problem without an additional z offset setting for the first layer. I tried nearly all settings for initial layer settings - it will not help.
When I discovered the z offset pulgin, i was quiet happy. Unfortunately, the plugin doesn't work at all. When I set a z offset that is not 0, the printer starts the first layer from approx. 10 mm height and the extruded filament just falls down on the bed. The Ultimaker S5 doesn't care what number is used for the z offset setting. As long as it is not 0, its impossible to print.
I had the same problem with older Ultimaker S5 firmware and Cura versions. So, I am running out of ideas and hope you can help me.