Maybe, it has something to do with this: cant update already published app after phonegap build
To summarize it: If you have set the android versionCode as widget attribute, an "8" was added to it by gradle. When setting "1" as versionCode, it became "18". "2" became "28" etc.
It seems like this has been fixed/changed. Now, the versionCode won't be increased by PGB.
To test it, append an "8" to you versionCode. (So again: If you have set your versionCode to "1", change it to "18". If you have set it to "2", change it to "28".)
If the update works now, it was caused by this change. If it doesn't work, please provide your config.xml.
Thanks, I wasn't using a versionCode attribute so I inspected the version codes generated by PGB and discovered the problem was indeed the spurious 8 on the end. Adding a specific versionCode has sorted it out.