Cubase randomly vanishes, losing focus issue?

I’ve been using Cubase 12 Pro for real now on paying sessions for about a month. It’s been generally excellent. One thing though: sometimes if I close a song, the whole application vanishes (and I am careful to make sure I close the song tab, NOT the top menu bar). And even more worryingly, if I’m working on a song and need to check something online for a client, opening another application can sometimes make Cubase vanish too. Again, without me closing the Cubase top menu tab. Not often, but maybe 1 time in 20. Anyone else have this happen? Thanks.