I’ve been plagued with ANT+ dropouts. Most days it was manageable, if obnoxious, but other days it was a complete write-off. I tried everything zwiftalizer recommended. I used a short USB extension cable (tried two), replaced batteries, moved fans, moved the cable, tried different USB ports, etc.
I moved the ANT+ dongle to a third cable after one really bad day of dropouts, and my Kickr quit dropping out, but my cadence sensor was worse.
After that ride, I used an in-line amp meter to test each cable and how well it charged my iPhone. The last cable I tried that worked the best was 0.5amps. The first two cables I had been using for awhile were 0.25 and 0.35 amps. So I had been using some 3 foot USB cables with high impedance.
I dug around and found an “Active” USB cable that is probably 15-25 feet long. It gave me 0.5amps charging my phone. So I used it last night and put the ANT+ dongle on the floor about a foot away from my crank.
I finally had zero dropouts!
So if you’re having ANT+ dropout issues and you’re pulling your hair out - try a high quality “Active” USB extension cable. (But not too long. I tried a 50’ active cable and only got 0.25 amps out of it).