I must have done something with my timeline and at some point I noticed that a chunk of clips in the timeline had no sound anymore (it was there before). If I double clicked on the video to bring up the clip on the source monitor, it would show as with no audio (sound icon greyed out). But the original file opened from the bin is fine.
Eventually I found a YT video offering a "solution": position the cursor on the clip I want to recover, select the clip on the timeline, select Sequence-Match Frame. At that point the clip opens in the source monitor and the sound is there as well. I can then drag the sound back where it was. Only downside now all those clips are "unlinked".
I would like to know what I did to create this issue as this is not the first time I noticed that.