Clone Stamp / Healing Brush error (graphics card issue?)

UPDATE: For anyone else having this problem, it seems to be the rulers that are causing this issue. As you can see in the video, the rulers are enabled, and from what I can tell, disabling the rulers prevents this issue from occurring

I've had an intermittent problem with both the clone and healing brush tools where the following problem happens:

1 - Option-click to define a source

2 - Start painting with the clone/healing brush

3 - As soon as the first brush stroke is made, the brush immediately creates a straight line stroke back to the location of the source as if the shift key was being held down OR the tool will lay down a single spot but will not continue painting until the mouse button or pen is released/lifted

Here's a video of the issue:

https://drive.google.com/file/d/1kzkSbbheOJZ9FUAXucHFlk8p-PjbVaQb/view?usp=sharing

The first issue (the straight line from the brush location to the source of the cloning) only seems to arise if the source is selected and then the clone brush is clicked quickly (i.e. going slowly prevents this from happening most of the time, but not always). The second issue is intermittent and I can't reproduce it as easily.

Again the issue happens with a wired mouse AND a wacom tablet so it appears to be either a Photoshop or OSX issue.

I have tried the following to try to isolate the issue. None of these attempts have resolved the issue:

1 - Set tip double click distance to zero in the Wacom settings

2 - reset all photoshop tools and preferences

3 - reinstall both wacom and mouse drivers

4 - create new user accounts

5 - bought a new tablet to see if my old wacom was the problem

6 - complete clean install of both OSX and Photoshop

The last step appeared to solve the issue brieflym but now it has returned after a few hours

I'm at my wits end and working under a tight deadline and all of the brush-oriented tools are basically unusable. I've had issues with this computer in the past, and over the summer Apple replaced the entire logic board under warranty (they would not tell me why)

System info:

Model Name: MacBook Pro

  Model Identifier: MacBookPro15,3

  Processor Name: Intel Core i9

  Processor Speed: 2.9 GHz

  Number of Processors: 1

  Total Number of Cores: 6

  L2 Cache (per Core): 256 KB

  L3 Cache: 12 MB

  Hyper-Threading Technology: Enabled

  Memory: 32 GB

Graphics

Intel UHD Graphics 630

Radeon Pro Vega 20

OSX Mohave 10.14.6