According to https://unifiedfontobject.org/versions/ufo3/glyphs/glif/#publicverticalorigin, the type of value for public.verticalOrigin should be integer or float.
public.verticalOrigin
This key is used for representing the “vertical origin” ‘y’ coordinate used for vertical layout. > The value for the key must be an integer or float> . This data is optional. Authoring tools can use this data and the advance element’s height attribute to create the VORG and vmtx tables.
However, in the .glif files, public.verticalOrigin is appended with type of string:
<lib>
<dict>
<key>public.verticalOrigin</key>
<string>880</string>
</dict>
</lib>
Please fix this issue.