I remember I ran into this issue a while back on my Win10Mobile device.. I was bewildered as to why my events kept disappearing after I hit save. I was and still am using Google Calendar, and when I checked my Google calendar on the web, the events would appear.
Just now, on my Windows 10 laptop, I browsed to June 2017, I got the same warning message that you did, Shamshi-Adad: "We're not able to show you some of the events in this time range. But they're still there--available via your account provider."
Is this a Google limitation? Or a Microsoft limitation? I find it frustrating. I upvoted the Windows Feedback to try to get this fixed...