Team Projects Disappearing

I work on a team where we are sharing dozens of team projects. I am frequently experiencing an issue where team projects that were previously shared with me disappear from my "Manage Team Projects" menu, so I am unable to access them. This happens for projects I have opened before, as well as projects that I haven't opened before. I often have the owner of the projects reshare them with me after they disappear, though they will sometimes disappear again within hours. 

Any assistance with this would be much appreciated. Thanks!!