@writersblock We are still investigating the cause of this. If you want to send log files from the problem computer to 'email@example.com' we may be able to add them to the ticket for closer examination.
@AshC checking if there are any new updates to this issue on Macs with version 188.8.131.5287. One of our support staff is asking, and I have asked for logs again in case more are needed.
I was using a 2012 macbook pro with an LG 4k monitor and had severe lag for weeks. So, I was finally able to switch my 2012 macbook pro out with a late 2014 iMac and I still have the LG 4k monitor connected. I do not have any lag with this configuration.