Saved Image Artifacts

I’m using Rawtherapee 5.8
On Mac 10.12.6

I was editing the playraw file found on pixls at this link:

Saving the file produced the following results:
pre-dawn-sun-boat-IMG_1598.CR2.pp3 (11.6 KB)

As shown, it occurs on two different file types (jpeg and png 8 bit) at two different resizes (2048w and 1024w). jpeg settings were quality: 90, subsampling: best quality

Not sure if it is related to this artifact, which can be seen at 100% viewing the rocks whilst editing:

Those white spots look like clipping indicator spots, but clipping indicator is turned off. Turning various modules off can remove some of the spots. Turning local contrast or ciecam02 off gets rid of them completely.