How to interpret inconsistent update icons in tray

[accounts0]

Sometimes I have this [1] red X icon obviously indicating something's out of date- this is clear enough.

Most of the time I have this [2] small green check icon which I assume means all is well. When I click it, there show no updates pending.

On rare occasions I have this [3] large green check, and I don't know what the difference between this & the other small green check is. Again, no updates show as pending when I click it.

Can someone explain?


[1]
https://imgur.com/rKb7N6e

[2]
https://imgur.com/csU07yv

[3]
https://imgur.com/rHDltci

[accounts0]

Have attached the linked images to save some clicks. Couldn't do so via a post edit, so they're here instead...

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[PaulW2U]

I don't recognise those icons from anything I've used in the past.

Which desktop are they from?

Edit: Looking at your other posts, Kubuntu.