Active channel with jitter 999.999

I am using Asterisk 17.5.1 and PJSIP.

When I look at the channel statistics for an active call to a specific device, I get a jitter of 999.999. When I look at the channel statistics for other active calls, I see typical values (e.g. RX Jitter - 0.000, TX Jitter - 0.000). I’m wondering under what circumstances would I get both transmit and receive jitter values of 999.999?

When I look at the source code, it appears as though I would only get this value if there is no jitter information returned from the channel statistics but, assuming this is correct, I’m not sure why this would occur.

channel stats command via cli:

pjsip show channelstats

Any insight would be greatly appreciated.