Intermittent test failure: dcp consumer flow control aggressive: Expected `20000000', got `YYY' - Flow Control Buffer Size not correct (4.9%)

Error signature

Failure of an engine_testapp test:

<pre>

Running [X/Y]: test dcp consumer flow control aggressive.../kv_engine/engines/ep/tests/ep_testsuite_dcp.cc:1928 Test failed: `' (Expected `20000000', got `YYY' - Flow Control Buffer Size not correct)

(X ms) FAIL

</pre>

Details
9 instances of this failure (4.9% of sampled failures):

• Time: 2020-11-26 10:08:59, Jenkins job: http://cv.jenkins.couchbase.com/job/kv_engine.ASan-UBSan/job/master/15268/, patch: http://review.couchbase.org/c/kv_engine/+/141044
• Time: 2020-11-26 20:25:08, Jenkins job: http://cv.jenkins.couchbase.com/job/kv_engine.threadsanitizer/job/master/7763/, patch: http://review.couchbase.org/c/kv_engine/+/140962
• Time: 2020-11-26 12:45:11, Jenkins job: http://cv.jenkins.couchbase.com/job/kv_engine.threadsanitizer/job/master/7730/, patch: http://review.couchbase.org/c/kv_engine/+/141044
• Time: 2020-11-25 17:23:41, Jenkins job: http://cv.jenkins.couchbase.com/job/kv_engine.threadsanitizer/job/master/7712/, patch: http://review.couchbase.org/c/kv_engine/+/141016
• Time: 2020-11-25 17:02:40, Jenkins job: http://cv.jenkins.couchbase.com/job/kv_engine.threadsanitizer/job/master/7711/, patch: http://review.couchbase.org/c/kv_engine/+/138903
• Time: 2020-11-25 15:52:44, Jenkins job: http://cv.jenkins.couchbase.com/job/kv_engine.threadsanitizer/job/master/7707/, patch: http://review.couchbase.org/c/kv_engine/+/140904
• Time: 2020-11-25 11:12:36, Jenkins job: http://cv.jenkins.couchbase.com/job/kv_engine.threadsanitizer/job/master/7690/, patch: http://review.couchbase.org/c/kv_engine/+/138766
• Time: 2020-11-24 09:27:02, Jenkins job: http://cv.jenkins.couchbase.com/job/kv_engine.threadsanitizer/job/master/7618/, patch: http://review.couchbase.org/c/kv_engine/+/140820
• Time: 2020-11-24 06:47:07, Jenkins job: http://cv.jenkins.couchbase.com/job/kv_engine.threadsanitizer/job/master/7613/, patch: http://review.couchbase.org/c/kv_engine/+/139882