Netgear rarely comments on such things. They do not want to be held to a schedule if there is an unforseen delay. But here are my guesses:
Debian Jessie is getting long in the tooth, and some or all of the software team is probably already looking for the next major upgrade to something newer. If no bugs or new security issues pop up, that might be the next update. But the effort required to do that is way more than a normal update. They have a lot of different archetectures it needs to run on, especially if they continue to support legacy hardware. Continuing to suport the 100 series with their limited RAM and processor is, I'm sure, a special challenge.
COVID-19 is likely affecting Netgear just like any other company. I have no idea whether they were already set up for from-home colaboration for such a project or not. You'd think that a corporation like Netgear would, but maybe they have reasons to not do so. Testing on actual NAS units could present some special issues here since some lock-ups could require on-site re-boot.
