Hi Mapper 7775,
I admire you using both in the field. I have used the juniper geode bluetooth and that works pretty well with both Avenza, Field Maps and Two Trails.
I bet your use of both Spike and Juniper on bluetooth is confusing the tablet.
What happens when you plug one of them in with a cable? That may be a good workaround. I remember the juniper has a hard wire connection.