"Can someone answer how long after dropping back below 5% threshold are entities required to amend their 13g filing?"
Just an educated guess:
That doesn't trigger a REQUIRED filing, but one can be made voluntarily.
The next required filing would be made on 2/14/22 if there was any change in the holding.
Remember the Aruda deal?
They were compliant in their disclosures.
As of 12/31/17 they held 7,316,824 shares (5.22%) based on their annual required filing made on 1/11/18.
As of 12/31/18 they held 6,266,824 shares (3.659%) base on their annual required filing made on 1/17/19.
No filings were made between those two filings even though at some point they obviously sold shares that got them below 5%.
More recently we saw a filing by Leviston showing 5.2%. Two weeks later they filed to show that they had sold down to 4.2%. The filing didn't say so, but I believe that filing was made voluntarily.
“I have had a wonderful time but this wasn't it.”
..........Groucho