Cannot initialize m2e so no Java projects compile

This doesn't always happen and sometimes I can fix it with Maven->Update Project..., and sometimes with a restart (with or without -clean). Sometimes it just won't go away.

When it happens I see a lot of these on startup:

In error log:

Plug-in org.eclipse.m2e.jdt was unable to load class org.eclipse.m2e.jdt.internal.JarLifecycleMapping.

In "Markers" (error shows up on POM):

Lifecycle mapping "org.eclipse.m2e.jdt.JarLifecycleMapping" is not available. To enable full functionality, install the lifecycle mapping and run Maven->Update Project Configuration.

– Configuration Details –
Product: Spring Tool Suite 3.6.4.201503100339-RELEASE (org.springsource.sts.ide)
Installed Features:
org.springsource.sts 3.6.4.201503100339-RELEASE