This happened to me too. I know this thread is a littler old now, just thought I'd add my voice in case someone is still struggling with it.
Between 1-3 September IG dealt with a hack, which was more of a bug exploit where hackers skimmed personal information from some 6 million accounts. The result was that IG dropped down an iron dome around each of those accounts.
Users had to log in, using 2-factor authentication via SMS, otherwise their accounts would appear deleted. What followed was nothing short of archaic mayhem as it seems IG was entirely unprepared for dealing with such an issue.
Some people never got the SMS code, some logins seemed to fail, some people were still missing posts and, most commonly, it seemed every one of those accounts suffered a shadowban. Mine was one of them.
I tried everything that every 'expert' blogger and grammer has ever posted about the shadowban, from disabling my account, to deleting and reinstalling IG, to staying inactive for over a week, to reporting it (like a crazy person), to filing a fake copyright complaint in an attempt to get attention, to trying completely new/fresh hashtags on new posts, to asking people who know people at IG, to using targeted ads pointing to facebook's offices to get attention, and ultimately I emailed IG's CEO (whose email address is on the web).
And let me tell you. NOTHING worked.
By Friday I was so pissed off because I get work from IG too, and I was really scared about how things might go - two weeks of having no engagement other than from followers, was a real pain. But then some comments started to surface of people getting restored after two weeks were up. And finally, last night, my account seemed to be restored as well.
I don't know how it goes with regular shadowbans, if it's a case of just waiting out the pain for 2 weeks or so, but in this case there was literally nothing a single user could do to get this fixed.
Hopefully now, though, this is resolved for everyone who had a vulnerable account.