Thanks Nate for the quick response! Good to know.
I had updated by copy/pasting the spine-libgdx/src directory, but hadn't deleted the old one (just overwrote the files), and looks like that may have caused an issue.
Additional question - do WeightedMeshAttachments not exist anymore? In my old spine version I see the file in com.esotericsoftware.spine.attachments.WeightedMeshAttachment.java. It isn't there in the new version, and I couldn't find any information about it being removed in the Changelog. Do we need to open our old Spine projects and re-export them, or something?
EDIT: Opening our projects with the new version of Spine, and then re-exporting them fixed the WeightedMeshAttachment problem. All is working! Thanks!!