No. It was a clear project on Unity 2017.3 and the only setting I changed was a .Net version. I ll dig a little bit and would let you know if something would show up. 

Should try that before writing a bug report, sorry. 
In a new project, SW is working perfectly, but it occurred to be so not because of 3rd party assets. A new project has by default a .Net 3.5 while I was using .Net 4.6. I changed scripting runtime version of the new project and the problem has returned. 

Using 4.6 is not vital for me so I'll get back to 3.5, thanks!

Can you please confirm, that you've got the message. If you have any other questions or maybe need some help with this bug, please don't hesitate to contact me.