Consistent frame jump from 0 to high repeat

Happens every second or so. The problem only seems to occur on Summoner’s Rift. The game is unplayable while this is happening. This is not a frame rate drop, it is like an on off switch for the frame rate and it happens every second or so. Is anyone else experiencing this? Are there any solutions? I have had this problem for a couple of weeks now and am running macOS Mojave Version 10.14.4 with the League Client V.9.10.273.9316 . Thanks.