Symptom:
ISIS adjacencies will not form for Overlay1 with the trigger provided in the Conditions section.

n7k-tb09-bldchk1-edge# sh otv isis adjacency
OTV-IS-IS process: default VPN: Overlay1   -------> All the adjacencies on overlay1 are down.
OTV-IS-IS adjacency database:
System ID       SNPA            Level  State  Hold Time  Interface Site-ID
 
OTV-IS-IS process: default VPN: Overlay2
OTV-IS-IS adjacency database:
System ID       SNPA            Level  State  Hold Time  Interface Site-ID
0000.0000.0003  0026.980b.fc42  1      UP     00:01:23   Overlay2 0000.0000.0001
0000.0000.0001  4055.3904.67c2  1      UP     00:01:36   Overlay2 0000.0000.0003
0000.0000.0002  4055.3923.dac2  1      UP     00:01:26   Overlay2 0000.0000.0002

Conditions:
Trigger: Change the join interface for Overlay1 to the same join interface for Overlay2.  This is essentially allowing two different Overlays to share the same join interface.

n7k-tb09-bldchk1-edge(config)# interface Overlay1
n7k-tb09-bldchk1-edge(config-if-overlay)# no otv join-interface Ethernet3/9/3
n7k-tb09-bldchk1-edge(config-if-overlay)# otv join-interface Ethernet3/12/3 <=== Join interface of overlay2