This is a complete drop out, nothing to do with the recent Garmin issues. Those were a different issue and had quite a unique signature i.e. a drop to half actual power for 2-4 seconds, with no change to cadence, all cadence data recorded was correct. If you look at your data in WKO+ or Golden Cheetah (due to plot resolution the extent of the problem doesn't show up well in Strava or Garmin Connect) you will see lots of the random half power values in your data up until you updated to 2.4, these should no longer be present in data captured since the update. I can confirm this is the case.
You should try several things to resolve your issue.
The manual will tell you a whole list of things to try but since your cadence drops as well, my 1st check would be the magnet, make sure it is in the right place radially and also in distance to the spider. It may have moved over time if the cable guide moves a tad when you shift, some do as they are held in place by a tab and the cable pressure rather than actually bolted in place. If it is not in the right place then the Quarq can not measure cadence and therefore can not calculate power.
If that fails, try a different battery. The battery should last ages, but you never know, you may have a duff one.
You can also check there is no moisture in the battery compartment and that the contacts are free of corrosion and not folded down too flat, they should make a solid contact with the battery.
The occasional drop out is inevitable. But if frequent there is something amiss.
If in doubt, contact Quarq, they are very helpful and usually respond pretty quick. Bear in mind they are on USA time when waiting for a response.