"Upcoming" tab doesn't load and lags the rest of the program

When I click the “Upcoming” sidebar tab to see upcoming tasks, it takes several minutes to load. In addition, the rest of the UI lags. For example, if I hover over “inbox”, it takes about 3 seconds for the “inbox” to turn to a lighter color of gray to signify I’m hovering over it. It also takes a few seconds to switch from upcoming to inbox or today for example, when normally it’s instant.