Calendar stopped syncing Windows Phone 8.1 with Outlook desktop Windows 10

[Windows Central Question]

I've been syncing a Windows Phone with my Outlook calendar and contacts for many years, but the last few weeks it seems to be not syncing events.

For example, two weeks ago I entered a new Calendar item for today on my phone, but it has still never appeared on the desktop. The item appears in the correct default "Calendar-Outlook" on the phone, in the same color as the default calendar items which have synced from the desktop. When I check the Calendar at outlook.live.com, the event appears correctly, in the same color as the rest of the default calendar items.

I have on my desktop PC: Windows 10, Outlook 2013, Hotmail Connector to sync. I do not have an Exchange account.

Phone is Lumia 1020 running Windows Phone 8.1.

T-mobile is my provider, which has been having multiple connection issues in my area lately, which might be unrelated, but voicemails and texts are delivered 1 to 24 hours late.

(I do not sync my email from Outlook to my phone, in case that is relevant.)

I tried to search for an answer on my own, but the search terms are too common. Any help would be very appreciated!

 

[jasonandrews25788]

I don't think T-mobile is causing this problem. Did you install or update something on your PC or Lumia device prior to this issue?
You could try using AkrutoSync at least to find out where's the problem. If syncing over Exchange server will fix the issue, try to reinstall Outlook or Outlook Hotmail Connector because I believe the one of those two might cause this problem.