Proxies lagging and choppy in premiere

[#1]

My proxies work in my sequence until I do something in the source window. Once I do that, the clips in my sequence become laggy and choppy. I tried downloading the previous premiere version but no luck. I just finished a project last week, the same workflow and everything was fine. Any idea of what's going on? I've attached a video of the process. 

Premiere Pro - 14.6.0

iMac (Retina 5K, 27-inch, Late 2014)

4 GHz Quad-Core Intel Core i7

32 GB 1600 MHz DDR3

AMD Radeon R9 M295X 4 GB

[#2]

Moving to the Premiere Pro forum from Using the Community

[#3 · Accepted solution]

I found a solution. For whatever reason closing the source window and then reopening it solved the problem.