Have you tried scheduling your post?

Sometimes this issue can occur when your Instagram Bot Follower and Instagram accounts timezones are not set the same. Try scheduling your post a few hours in advance to see if this will resolve the missing caption/first comment issue.

Have you tried using a new proxy address?

With the latest Instagram anti SPAM API changes, your Instagram account may have received a low trust score. In order to get around this and improve your account trust score, you need to use a custom proxy.

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