Zigbee meshes take time to heal. Small meshes (less than 10 devices) usually take about 1-2 hours to fully heal and propagate routes. So, if you move the devices closer to your hub, you’ll want to wait at least an hour or two before thinking that the results are accurate.
Further, FoH devices are ZLL profile devices. The reason they work will with the Hue hub is that the Hue hub is a fully certified ZLL profile compliant controller. Other controllers like the Conbee II, CC2531, and others support both ZLL and ZHA meshes, but you may experience issues as there are distinct differences in the two profiles when it comes to messaging. Your Osram plug is (I’m guessing) a Smart+ plug, which means that it is a ZLL profile device that you have on a ZHA profile controller. Most likely what’s happening here is that the ConbeeII is sending messages using the ZHA profile (as it should because you have a mix of ZLL and ZHA devices) and the Osram plug may be mangling those messages during re-transmission to the switches.
If they are working well on the Hue hub, I’d leave them there and just keep your Aqara sensors on deConz. I actually run this type of setup: For my Ikea bulbs (which tend to SUCK in a ZHA mesh), I have them paired to my Hue hub. All the rest of my sensors (contact, motion, humidity, etc) are on my ZHA mesh hosted by HA (using a Nortek stick). What this does is allows devices that use the ZLL profile to stay on ZLL and my ZHA profile sensors stay on the ZHA mesh. This way, there’s no mangling of messages. I haven’t had a single device drop off either network (aside from an Ikea Driver that actually went bad) in years now.
As long as you are using two different channels for your meshes, they should work fine together.