Migrate from mlab on parse server error on app connect

i migrated a dev app and a prod app from mlab and both migrations success on not very large DBs.

connect to both OK using mongo shell ( 3.6 )

but both failing on app connections

Im more concerned about fix to the prod app ( heroku , node webapp with parse-server )

stdout from heroku log below:

2020-06-03T01:09:07.489591+00:00 heroku[web.1]: State changed from starting to up
2020-06-03T01:09:08.389099+00:00 heroku[router]: at=info method=GET path="/parse/health" host=warm-earth-97740.herokuapp.com request_id=512b98e5-7673-4f2e-a5ea-403065f5f700 fwd="" dyno=web.1 connect=0ms service=16ms status=200 bytes=639 protocol=https
2020-06-03T01:09:37.327864+00:00 app[web.1]: MongoServerSelectionError: Authentication failed.
2020-06-03T01:09:37.327872+00:00 app[web.1]: at Timeout._onTimeout (/app/node_modules/mongodb/lib/core/sdam/topology.js:430:30)
2020-06-03T01:09:37.327873+00:00 app[web.1]: at listOnTimeout (internal/timers.js:549:17)
2020-06-03T01:09:37.327873+00:00 app[web.1]: at processTimers (internal/timers.js:492:7) {
2020-06-03T01:09:37.327875+00:00 app[web.1]: reason: TopologyDescription {
2020-06-03T01:09:37.327876+00:00 app[web.1]: type: 'ReplicaSetNoPrimary',
2020-06-03T01:09:37.327877+00:00 app[web.1]: setName: null,
2020-06-03T01:09:37.327877+00:00 app[web.1]: maxSetVersion: null,
2020-06-03T01:09:37.327878+00:00 app[web.1]: maxElectionId: null,
2020-06-03T01:09:37.327878+00:00 app[web.1]: servers: Map(2) {
2020-06-03T01:09:37.327879+00:00 app[web.1]: 'ds015044-a0.mlab.com:15044' => [ServerDescription],
2020-06-03T01:09:37.327879+00:00 app[web.1]: 'ds015044-a1.mlab.com:15044' => [ServerDescription]
2020-06-03T01:09:37.327880+00:00 app[web.1]: },
2020-06-03T01:09:37.327880+00:00 app[web.1]: stale: false,
2020-06-03T01:09:37.327880+00:00 app[web.1]: compatible: true,
2020-06-03T01:09:37.327881+00:00 app[web.1]: compatibilityError: null,
2020-06-03T01:09:37.327881+00:00 app[web.1]: logicalSessionTimeoutMinutes: null,
2020-06-03T01:09:37.327882+00:00 app[web.1]: heartbeatFrequencyMS: 10000,
2020-06-03T01:09:37.327882+00:00 app[web.1]: localThresholdMS: 15,
2020-06-03T01:09:37.327882+00:00 app[web.1]: commonWireVersion: null
2020-06-03T01:09:37.327883+00:00 app[web.1]: }
2020-06-03T01:09:37.327883+00:00 app[web.1]: }
2020-06-03T01:09:37.339659+00:00 app[web.1]: npm ERR! code ELIFECYCLE
2020-06-03T01:09:37.339931+00:00 app[web.1]: npm ERR! errno 1
2020-06-03T01:09:37.340761+00:00 app[web.1]: npm ERR! parse-server@4.2.0 start: `node ./bin/parse-server -- lib/conf.json`
2020-06-03T01:09:37.340850+00:00 app[web.1]: npm ERR! Exit status 1
2020-06-03T01:09:37.340957+00:00 app[web.1]: npm ERR!
2020-06-03T01:09:37.341032+00:00 app[web.1]: npm ERR! Failed at the parse-server@4.2.0 start script.
2020-06-03T01:09:37.341107+00:00 app[web.1]: npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

Hi Robert,

The mLab Support team (support@mlab.com) has reached out to you to help you with this issue in mLab Support ticket #185922. Please check your inbox for an email from support@mlab.com.

We look forward to helping figure this one out in that context

Any chance you could share how you fixed this? I have the same issue. Thanks.