I can't hear previous track when recording new track

I’m using Audacity 3.3.3, Windows 10 and a Behringer USB interface.
I can record the first track – drums, say – just fine.
However, after I create a second track and hit record for a bass overdub, I can hear the bass but not the drums from the first track.
I can hear the drums and bass [out of sync of course] when I hit play.
I’ve used Audacity for years and made many multi-track recordings but now, after returning to Audacity after a time, I’m stumped right off the bat.
Why can’t I hear the other track?
Perhaps a software update changed something I need to know about.

I don’t do audio recording much, besides a Voiceover of my gameplay videos! I especially DON’T record music, so I’m not sure how this applies to your knowledge already! BUT. I do record a voiceover of my own videos, in one of two ways;
Using one computer, I’m watching the video I’m talking about/over, using Win Media player to play the video on my computer screen, while second app (Audacity) is running on same machine. I have my headset setup as input for Audacity, and the Headset still playing audio from the video I’m watching. I basically hit record, than telling myself what I’m recording over (what video the voiceover is for), and I tell myself recording, that I’m hitting play in 3… 2…1 and a second after I hit play, i begin talking.
It records my voice just fine. but often the video in the background from the TV output (my laptop actually plugs into a smart TV with HDMI, huge screen, different topic), and the alignment usually works just fine, but it sounds like two feeds of the same audio, back in Shotcut (my video editor).

This is usually solved, if I use a second computer, and turn the volume down on the TV, and the headset is plugged into second computer, so I don’t hear the audio of the video through the headset, just barely heard on TV (headset covering ears, muffles it a little).

Either way, once recording is done, I stop both video and recording, and save/ export in Audacity as MP3, and back on my Shotcut setup I simply load the Mp3 file, and line it with the in game audio, and usually it’s all there lined as I want…

ALL this for you? Again. I don’t record music, or much of anything else. I can suggest if your recording different instruments on different feeds, using a media play back option to play your audio back to you while recording second audio. If you’re doing multiple instruments as it sounds, record your drums first… and using second media app, play back the drums while recording second instrument. Than line both up however you put them together, even in Audacity. Export those as one track, so both are recorded into one. Than play that back while recording 3rd instrument, etc. and it should work! I think! I’m no tech genius!

Hopefully with what I said here, someone else can add more input!