Unumbered frames in the Timeline/Dopesheet !

Hi all,
the image here says it all: I have unnumbered frames in my animation, for instance here between frame 83 and 84 !
Any advice to solve that ? Note that I cannot select these unnumbered frames.
Thank you

You can change your snapping and then just grab and release to snap them to the nearest frame.

Thanks a lot !!
I still have to figure out what these options are, I was really annoyed. Thank you again