I have a lot of missing dates on my google timeline, not sure why this has occurred though I am sure that my location is on.
Is there any other product that I can view my timeline with other than google so that I can see the missing dates?
If they aren't on the Google information, then other things would not be able to see them either, since the information comes from Google's system.
It is possible you are in areas that are blocked (it happens) or are not shown. It is also possible that they are not showing on the phone, but would on your timeline if viewed from a computer. I would check that way first, and if still missing, then contact Google.