If you reset statistics using hcimsiutil -Z while msgs are queued, negative numbers can be the result. Also, there was a bug that allowed the numbers to occasionally go to negative. Not sure if it was ever fixed.
But, will this negative queue depth result in loosing records. Because we had negative queue depth of -299 and I stopped and started the thread twice and second time it went to 0 but first time it didn’t make any difference. Infact the depth kept on increasing.