Based on BF-26526.

For example this test: https://github.com/mongodb/mongo/blob/a7cda0d9cf32b7074b4c9a2efe6e6590b4dab564/jstests/core/txns/speculative_snapshot_includes_all_writes.js
1. Setups fail point.
2. Starts parallel shell to hit the fail point.
3. In main shell uses checkLog to find line about hitting the fail point.
4. Checks stuff

It can fail when between steps 2 and 3 too many events will happen so message about hitting the fail point will be pushed out of RAM log cache.

To avoid it, we need to replace checkLog with waitForFailPoint command, created specifically for this case: https://github.com/mongodb/mongo/wiki/The-%22failCommand%22-fail-point

Also, we should check other tests that may contain similar problems.