Not all FX channels not showing up on send list :(

I created a template from scratch, setting up various FX channels with reverbs, delays, etc. On some tracks in the template, when I click the “Select Destination” on a send, some of the FX channels are not on the list. If I create a NEW track, the FX channel is listed. This was happening in N5 so I made my template from scratch in N6. Is this because sends can only be routed to subsequent channels or what?