Appreciate the quick reply, @matt1!
You were right. Deleted the 1.2.0 Paho from Add-Ons, cleaned cached, rebooted and I once again have both MQTT2 and espMilight.
Ran bundle:list from the console after the remove and reboot, looks like I have Paho 1.2.1
Without your 1.2.0 Paho, did see this error:
==> /var/log/openhab2/openhab.log <==
2019-07-22 16:25:24.636 [DEBUG] [ell.impl.action.osgi.CommandExtender] - org.openhab.binding.espmilighthub (206): Starting destruction process
2019-07-22 16:25:24.637 [DEBUG] [ell.impl.action.osgi.CommandExtender] - org.openhab.binding.espmilighthub (206): Not an extended bundle or destruction of extension already finished
2019-07-22 16:25:24.662 [WARN ] [org.apache.felix.fileinstall ] - Error while starting bundle: file:/usr/share/openhab2/addons/org.openhab.binding.espmilighthub-2.5.0-SNAPSHOT.jar
org.osgi.framework.BundleException: Could not resolve module: org.openhab.binding.espmilighthub [206]
Unresolved requirement: Import-Package: org.eclipse.paho.client.mqttv3; version="[1.2.0,2.0.0)"
at org.eclipse.osgi.container.Module.start(Module.java:444) ~[?:?]
at org.eclipse.osgi.internal.framework.EquinoxBundle.start(EquinoxBundle.java:383) ~[?:?]
at org.apache.felix.fileinstall.internal.DirectoryWatcher.startBundle(DirectoryWatcher.java:1260) [10:org.apache.felix.fileinstall:3.6.4]
at org.apache.felix.fileinstall.internal.DirectoryWatcher.startBundles(DirectoryWatcher.java:1233) [10:org.apache.felix.fileinstall:3.6.4]
at org.apache.felix.fileinstall.internal.DirectoryWatcher.doProcess(DirectoryWatcher.java:520) [10:org.apache.felix.fileinstall:3.6.4]
at org.apache.felix.fileinstall.internal.DirectoryWatcher.process(DirectoryWatcher.java:365) [10:org.apache.felix.fileinstall:3.6.4]
at org.apache.felix.fileinstall.internal.DirectoryWatcher.run(DirectoryWatcher.java:316) [10:org.apache.felix.fileinstall:3.6.4]
Edit - Did find this earlier today, seems like it could be applicable: https://github.com/openhab/openhab-core/pull/929
Edit 2 - And this is the bump from 1.2.0 to 1.2.1 in the core compile pom: https://github.com/openhab/openhab-core/commit/d55d59d3b5e0e7ca0ea1efd95bd61e809c8cfb78