This is a known problem and the team is working to solve the issues - I find that starting a New Plan View Window also works when this starts happening - you can then delete the original plan view Window where you were having the problems.
I believe personally that this is caused by Lineweights and having your Highlight Line width settings something other than defaults - at least in part. I have been working this am ad have seen that sometimes the flash occurs and the line briefly highlights then no longer highlights - but if you close the command the line is highlighted
I have also been seeing dual highlights as well - i.e. Sometimes a line will highlight in a color other than what I have selected - it also sometimes shows me two colors - I use lime green as my highlight and I still see Orange as well
Alan