Assertion failed: 200138 (17.0.10.6285) - any ideas?

[Breck_Carter]

This "can't find values in index" assertion 200138 happens from time to time, on the same index in completely different database instances in completely different environments.

Confidence is high that it's not a data corruption error caused by disk or RAM... because it's always the same table, same index, in different database files created at different times on different continents.

Sometimes it's just the Assertion, sometimes the Assertion is accompanied by the "forbid mutex" stuff.

E. 07/20 17:48:10. *** ERROR *** Assertion failed: 200138 (17.0.10.6285)[f]
Can't find values for row bbc3f:c in index 'ux_long_varchar'
W. 07/20 17:49:10. Task 000002857F6DB3A0(Request task 878) is trying get forbid mutex held by task 000002857F6DD920(Request task 876) for more than 60000 ms
W. 07/20 17:49:10. Task 000002857F6DD920(Request task 876) state: worker=000002857F6F4430 wakend=0 waiting=2
W. 07/20 17:49:10. Worker 000002857F6F4430 state: wakend=0 waiting=0 in_atomic=0 is_dedicated=0 in_critical_section=0 allow_forbid=0

Here's a mysterious fix made earlier...

    ================(Build #5874  - Engineering Case #819665)================

    Under some conditions, the server may abort after printing a message like 
    below to the console or print another message line with 
    incorrect information.

    Task 0x245bda0(Request task 52) is trying get forbid mutex held by task 
    0x2460ea0(Request task 79) for more than 60000 ms

    This has been fixed.