I am using LMMS 1.2.0 RC6 (64bit) on Windows 10 version 1803. I loaded the free Native Instruments Realtor 6 (version 6.2.2) into LMMS (through vestige) , and part of the interface was missing. This happens only for the "Lazerbass.ens' patch on Realtor 6. (I'm sorry I don't know how to upload the screenshot here).
Fix that first:
http://lmms.io/forum/viewtopic.php?f=1&t=4740
Scroll down..
Asa i saw your issue i sighed.. not a 1.1.3 on win10 again, because that causes exactly that problem, since a winUpdate in May
Buuut..
You say you are on RC6 (:!)
That is ..strange
I can only say, that i do not know the plugin, and perhaps its just nogood in lmms