Due to an issue on Instagram's side, new Сontacts from Instagram are getting automatically deleted now as the bot tries to send them a message.
This issue is already reported to Meta, we recommend subscribing to this report for updates: https://developers.facebook.com/support/bugs/559090092557779
We've just released a temporary fix as a workaround which would keep newly subscribed IG Contacts intact in your ManyChat account, however Instagram messages will not be sent to them until Meta's team fully resolves the issue on their side.
More information to follow soon.