I just updated to the latest version, but I occasionally noticed this issue over the past month or so in the previous version. After a few minutes of work, the Finder—not just LR—will start flickering white, both spontaneously and with just the slightest movement of the mouse. Restarting the computer used to solve the problem but now it has no effect. The same flickering also occurs in PS, but it's multicolored, not white. Still on OS 10.14.6. The phenomenon doesn't occur in any other app.