Well, in each part of the macro you had 2× Resize Image to 600×600 and 1× Resize Image to Fit 600×600, so you are resizing the image 6 times (!), and writing it 2 times as JPEG.
(You are aware that JPEG is a lossy compression, right? With each compression run you loose quality.)
I threw out all the duplicate actions, and it still works here.
Besides the literal duplicate actions, what is the point in combining a Resize Image with a Resize Image to Fit action (with the same dimensions)?
Indeed, when several (or maybe all?) macros stop working at the same time, then most likely KM Engine has some fundamental problems to do its job.
I tend to think this too. You could create a fresh user account, and see if the issues happen there, too. But since it seems to be intermittent, this can become time consuming.
There is a troubleshooting post about permissions, in case you haven’t seen it yet: