The retaining ring is used for pressing the driver into the pill.
The ring sits on the spring side of the driver, the contact is on the “in”side of the driver.
The driver has to make contact with the pill in order to function. Always.
That’s why we always ask first: have you checked if the retaining ring is screwed in properly?
A regular Nanjg driver maximally has room for 8 regulators. The well known AMC7135.
As a rule the first 4 regulators are placed on the inside of the driver. The others on the outside.
If there is more than 4*AMC7135 regulators, like 6*AMC7135 or 8*AMC7135,
the AMC7135 block’s make it impossible for the retaining ring to get into the threads of the pill.
You have noticed that already.
The quick and easy solution is to solder the driver board into the pill.
Almost always good contact, leading to a good flow of electricity and of heat.
Minus point: because of capillary properties of the flowing soldering paste quite hard to remove.
There is a more elaborate workaround.
Grind out the inside (NOT the threads) of your retaining ring.
That way the ring (cupping the AMC7135’s) can reach the threads on the inside of the pill.
This is a LINK to a thread were (also) several other solutions are proposed.