Adapter works on some coax outlets but not another?

I have Verizon Fios with the G3100 router. The following picture shows the [brand-new] splitter with ONT box -> IN:

As you can see, 1 of the 6 ports is capped with a terminator. The other 5 ports go to coax outlets in the following rooms with their respective connections (which all work perfectly) as of right now:

- study: G3100 router (connected to ONT on both ethernet (WAN port) and coax (LAN lights up))

- living room: Fios TV One

- master bedroom: Fios TV One Mini

- guest bedroom: goCoax WF-803M [->ethernet->TP-Link RE450 in Access Point mode]

- basement: unused [capped with terminator]

I have a second goCoax adapter. I wish to use it in the master bedroom -- ultimately by adding a 2-way splitter there to allow for the coax outlet to serve both the Fios TV set top box as well as the goCoax for an ethernet connection; but for now I'm just seeing if at least I can get the MoCA signal from that outlet without even splitting.

I have tested the adapter successfully by connecting to the internet via ethernet->adapter->basement coax outlet, even while the guest bedroom adapter is also connected. So as it appears, the number of connections isn't an issue. However, when I instead test it the same way by connecting it to the master bedroom coax outlet (i.e. completely disconnecting the Fios TV connection), the same way I did in the basement (which I re-capped), the MoCA light does not turn on.

I'm still learning how all this works so any insight and advice would be appreciated!! Thank you so much!