My personal opinion is that ANT+ is far superior to Bluetooth.
Use Zwiftalizer.com to look at your log file you may find some information.
Also if you use bluetooth try to eliminate unneeded bluetooth devices like headphones, speakers or other phones.
Also check your Wifi router channels.
Zwift can only work with what is send to it and that is all hardware dependent.
Zwift is very susceptible to dropouts because it has to be interactive and that is why we like Zwift.
If it was just a graph on a screen the software could reed every 10 seconds and average the data and update the screen every 30 and no one would care.