Spacebar-preview not working

Since upgrading to Mojave on my MBP13 TT3 2017 I can't preview photos in the Photos App with spacebar as I used to in High Sierra and earlier. When selecting a thumbnail and clicking spacebar I hear the alert sound but nothing happens. Wright now the only way for me to see the full photo is by double clicking it.

For the record, I keep photos ON the Mac (Download Originals to this Mac is ON).

I verified with the support pages for Mojave and it says this still should be possible.

Spacebar-preview works just fine in Finder (when previewing images too!). It doesn't work in Photos only.

How do I fix this?