When using mongostat's -o option to customize output, I've seen a few cases where the column output for a field where the diff() function is used transitions from a valid number to "INVALID".

For example, if I look at cursor insert operations with this command:

mongostat -o "wiredTiger.cursor.cursor insert calls.diff()= cins,time"

I see output transition like this:

{{9404 Apr 4 20:57:01.860
10759 Apr 4 20:57:02.860
11059 Apr 4 20:57:03.861
12034 Apr 4 20:57:04.860
12349 Apr 4 20:57:05.876
10423 Apr 4 20:57:06.876
9545 Apr 4 20:57:07.863
11069 Apr 4 20:57:08.861
9979 Apr 4 20:57:09.862
cins time
INVALID Apr 4 20:57:10.860
INVALID Apr 4 20:57:11.861
INVALID Apr 4 20:57:12.862
INVALID Apr 4 20:57:13.861
INVALID Apr 4 20:57:14.861
INVALID Apr 4 20:57:15.874
INVALID Apr 4 20:57:16.861
INVALID Apr 4 20:57:17.861
INVALID Apr 4 20:57:18.862
INVALID Apr 4 20:57:19.860}}

Looking at the raw counter value for cursor insert calls, I see that it was 1072355130 at 20:55 and 1075659772 at 21:00, so I'm not sure why subtracting intermediate values would generated an error.

I have seen this happen with other fields too, for example wiredTiger cache page requests.