MSP432 Programming and boundary scan issues (4-Wire, 2-Wire and SWD)
The 4 wire (JTAG) mode is slightly more reliable from an electrical point of view, each wire is driven as either input or output (and never high impedance). SWD mode has a clock, and a bi-directional data signal. It is also designed to rely on the pull-up being present on SWDIO (this is not SWO, that is a different, but similarly named function).

You might get some (or unreliable) communication if the pull-up is missing, but I think this is data dependant (regardless of clock speed). It could be enough to complicate your observations though.

However, if the JTAG pins have been re-claimed for functional use, modern tools should have no problems connecting over SWD (in the early days, tool support was sometimes better in JTAG mode).