What is the cause of these colored dots?

I recently bought a used Canon 6D with the 24-105 f/4 L USM kit lens. After shooting some outdoor pictures at night, I noticed some colored pixels or dots in the images, especially at longer exposures (10-30s). I have made some test shots with the lens cap attached to show these dots (the area stays the same):

ISO 2000, 30s:

ISO 500, 30s:

ISO 500, 15s:

ISO 500, 5s:

ISO 500, 1s:

I have also looked at the following posts:

• What is the source of this multicolored noise in these samples?
• Are these stars or noise?
• Longer exposure & lower ISO or shorter exposure & higher ISO – what gives better results when photographing stars?
• Star photography noise

From what I’m gathering this is most likely some kind of noise (may thermal?) due to the long exposure, but this doesn’t look like the usual noise I’ve seen before with higher ISO values. Could these dots be stuck pixels?