JH> For some reason when I run ./mutil nodelist.ini Mystic will import every
 JH> nodelist except for Micronet's.
 JH> 
 JH> Contents of fdn_MIN_LIST:
 JH> MICRONET.ZIP  (Contains micronet.304 & file_id.diz)

There is your problem. The Mirconet nodelist isn't in the proper format as per
the nodelist spec. It should be named MICRONET.Z(last two digits of the day of
the year), for example, if the archive contains micronet.304 then it should be
named micronet.z04.

You can see that the other two nodelists you mentioned are in the proper
format:

 JH> Contents of fdn_FSX_NODE:
 JH> FSXNET.Z11   (Contains FSXNET.311)
 JH> 
 JH> Contents of fdn_NODELIST:
 JH> NODELIST.Z04  (Contains NODELIST.304)
 JH> NODELIST.Z97  (Contains NODELIST.297)

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--- Mystic BBS v1.12 A47 2020/10/31 (Linux/64)