Wondering if anything in Apple Support's articles can help:
My Photo Stream - Apple Support
says:
"If you're using My Photo Stream instead of iCloud Photos,
your photos or videos might appear to be missing"
(says: Go to Photos > Albums > My Photo Stream.)
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About iCloud Photos and My Photo Stream - Apple Support
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If My Photo Stream isn't updating – Apple Support
Eg: says (on Mac) : "Open the Photos app.
Then choose Photos > Preferences. Click iCloud (or Photo Stream).
Make sure that My Photo Stream is selected."
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If you have multiple libraries in Photos, you may have to designate one for My Photo Stream.
Designate a System Photo Library in Photos – Apple Support
says:
"The System Photo Library is the only library that can be used
with iCloud Photos, Shared Albums and My Photo Stream"
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If you still need help, you might want to try reaching out to the Photos Support Team:
There is a "Get Support" link (at the very bottom), of their website (link below)
Photos - Official Apple Support
All the best :-)