Page 124 of the manual:
For all other PROFILER variants, the Auxiliary Input cannot be used while you have an Effect Loop active in your Rig, or while you are in PROFILER Mode, as the physical inputs are needed for a different purpose.
If you use a mono loop, you only use the DIRECT OUTPUT/SEND and RETURN ports. So, the MONITOR OUTPUT and ALTERNATIVE INPUT could still be available (since it's a mono loop). That would give the possible to use the mono external effects loop in conjunction of e.g. a looper using the monitor output and alternative input (maybe setting the AUX input).
Is there no way to give this possibility in a future update?