Yes, you are not alone. I've been having the same problem, started mid-way through 2014. I didn't think anything of it at the time, but wish I had.
I've also gone through multiple rounds with Apple Support only for them to repeatedly tell me that I have no GPS data in 2014 pictures, despite the fact that the vast majority do have GPS data.
A few months ago the same thing happened to me with 2015, lost location information in 'Years' view. I realised this was related to importing a series of photos from my GoPro, and after deleting them all from my library, adjusting GPS EXIF data and re-importing (this was before Photos for Mac supported editing GPS data directly), the issue went away.
I suspect the issue is down to a selection of images that do not have GPS data / have invalid GPS data, causing something in Photos to barf.
Reading https://discussions.apple.com/thread/7174772?start=0&tstart=0 has led me to believe that it may be possible to create a smart album for all photos in 2014 that do not have GPS data. If so, then it can lead to one or more of the following options:
- Export all untagged images, re-importing one at a time and identifying which image causes the library to stop summarising for the year
- Identify a tipping point, if it's over a certain % of untagged images that causes the library to stop summarising for the year
- Manually tag all the untagged images, where relevant, if it's a % issue.
- Delete some images.
Sorry I don't have anything more helpful to report, but at least you know you're not alone! :-)
If you do make any progress on any of the above, please to share. I will also share if and when I'm able to identify anything further.