Intermittent failure in engine_testapp "mem stats" - Exceeded maximum wait time of 60000000us waiting for stat 'ep_items_rm_from_checkpoints' to change from 0

Error signature

Failure of an engine_testapp test:

<pre>

Running [X/Y]: mem stats...Exceeded maximum wait time of 60000000us waiting for stat 'ep_items_rm_from_checkpoints' to change from 0 (last value:XXX) - aborting.

</pre>

Details
25 instances of this failure (43.1% of sampled failures):

• Time: 2022-03-10 11:16:15, Jenkins job: http://cv.jenkins.couchbase.com/job/kv_engine.linux/job/neo/52/, patch: https://review.couchbase.org/c/kv_engine/+/172037
• Time: 2022-03-08 11:58:23, Jenkins job: http://cv.jenkins.couchbase.com/job/kv_engine.linux/job/neo/27/, patch: https://review.couchbase.org/c/kv_engine/+/171649
• Time: 2022-03-08 12:35:16, Jenkins job: http://cv.jenkins.couchbase.com/job/kv_engine.linux-CE/job/neo/30/, patch: https://review.couchbase.org/c/kv_engine/+/171920
• Time: 2022-03-08 11:58:24, Jenkins job: http://cv.jenkins.couchbase.com/job/kv_engine.linux-CE/job/neo/28/, patch: https://review.couchbase.org/c/kv_engine/+/171744
• Time: 2022-03-08 11:58:23, Jenkins job: http://cv.jenkins.couchbase.com/job/kv_engine.linux-CE/job/neo/27/, patch: https://review.couchbase.org/c/kv_engine/+/171649
• Time: 2022-03-08 10:11:37, Jenkins job: http://cv.jenkins.couchbase.com/job/kv_engine.linux-CE/job/neo/26/, patch: https://review.couchbase.org/c/kv_engine/+/171451
• Time: 2022-03-10 11:16:15, Jenkins job: http://cv.jenkins.couchbase.com/job/kv_engine.macos/job/neo/55/, patch: https://review.couchbase.org/c/kv_engine/+/172037
• Time: 2022-03-08 12:35:16, Jenkins job: http://cv.jenkins.couchbase.com/job/kv_engine.macos/job/neo/32/, patch: https://review.couchbase.org/c/kv_engine/+/171920
• Time: 2022-03-08 12:35:16, Jenkins job: http://cv.jenkins.couchbase.com/job/kv_engine.macos/job/neo/31/, patch: https://review.couchbase.org/c/kv_engine/+/171451
• Time: 2022-03-08 11:58:24, Jenkins job: http://cv.jenkins.couchbase.com/job/kv_engine.macos/job/neo/30/, patch: https://review.couchbase.org/c/kv_engine/+/171744
  <cut> - only showing details of first 10/25 instances.