Cakewalk Team,
I've not encountered this issue before so I feel it maybe related to Jamaica Plain 21.9.00 build 40.
I created a buss for grouping instrument tracks, then another buss for a master then out to the soundcard.
I found that the panning laws in the track were not registering through the buss. The tracked worked perfectly with out going through the buss.
I could pan through the buss but anything i did in the track didn't translate to the buss.
Once i clicked on the mono (on the buss) and then clicked again to return to stereo it started working.
Strange bug
 
P.S. - Is this where i should report bugs like this??

Can you find out/rule out whether a specific plugin or soft synth causes this behaviour please?

The first time i noticed it i was just running "Positive Grid's, Bias Desktop" 
64bit plug for guitar.
Track>Buss>Soundcard
As i said tho, never had this issue before.
Mind you, windows 10 pro just had a major update too. mmmmmm that could potentially the issue also.
 

Maybe the option to set the send pan to mirror the source track has something to do with this? Right-click the Send Pan control and choose Follow Bus Pan from the pop-up menu. This setting is only active when the send has the same interleave as the bus it feeds into, and is set to Post Fader. If enabled, the Send Pan control no longer affects the output.