Are the tiny bubbles coming from the threat of this return eyeball indication of a leak?

I got this tiny bubbles seem to be coming from the thread area of the deep end return eyeball. I do loose about 1/4 to 1/2 inch of water a day depending on how hot it gets. Have always assumed it was due to evaporation. But now this little bubbles have me concern that I might have a leak.

Anyone have experience the same?

Inground Vinyl SWCG pool, 4 returns (only one with tiny bubbles furthers from the pump at deep end) two skimmers. One split main drains.
[ATTACH...

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