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Possibly rep score. I think there's a minimum, maybe 55 (to avoid spam). @lisamgentile1961 had the same issue I think with one of her accounts

Although I think hers didn't post at all rather than not go up top, so maybe some other glitch!

so what can they do to solve it?

No idea. That would be a question for them, so hopefully they will see your feedback and either sort it for you or give you an answer.

Yes, I still am having that issue. I need to make some time for that account to increase it's reputation.