ATSAMD21G18A TransferError: No ACK received

Problem
I'm trying to use pyOCD with an ATSAMD21G18A connected to an nEDBG CMSIS-DAP, but any command I try results in the following error:

pyocd.probe.pydapaccess.dap_access_api.DAPAccessIntf.TransferError: No ACK received

Possibly useful info

1. When I start pyocd commander I get Connected to ATSAMD21G18A [Lockup]: MCHP3313031800000599. I'm not sure what [Lockup] means in this context.
2. I note that the ATSAMD21G17D is provided by Microchip.SAMD21_DFP.3.6.144 but the ATSAMD21G18A is provided by Keil.SAMD21_DFP.1.3.1, which is deprecated. Perhaps this is a pack issue, but I don't know how to change it.

Background
The Curiosity Nano board has a built-in nEDBG adaptor and an ATSAMD21G17D target MCU on-board. I was able to connect to this chip fine using pyOCD, however I now want to use the nEDBG adaptor to program an ATSAMD21G18A chip on a different board. I cut the SWD traces on the development board, as described in the user guide, and connected it to my target processor, but pyOCD refuses to play.

Atmel (Microchip) Studio running on the same machine with no change to the hardware setup works perfectly, so I'm confident it isn't a hardware issue.

I'm using a MacBook Pro (Ventura), running pyOCD natively. I run Atmel Studio using Parallels.

Start by reproducing the connection through the pyocd commander entry point and inspect the DAPAccessIntf.TransferError path for the ATSAMD21G18A. Compare the Microchip.SAMD21_DFP.3.6.144 and deprecated Keil.SAMD21_DFP.1.3.1 device-pack details mentioned in the report. Done means commands reach the target without a “No ACK received” error.