Just tried to install 22 May 1.5.6, the installer told me it cannot install because there is already a version installed that I need to uninstall manually (was pre-22 may 1.5.6)
So I did uninstall and then reinstalled 22-may 1.5.6 but got error message telling tcp port 8120 was already used.
So I tried to undertsand and the strange thing is that in fact some no more existing process (I suppose it was NCS 1.5.6 pre-22 May) is still binded to those TCP ports.
I am using Win10 64bits and this is really amzing I never saw such situtaion, I tried to deactivate network card but still did not release the listening TCP ports.
I will reboot the PC that will fix the problem but just wanted to tell about this weird sitiuation.