Upgrading Ubuntu from 16.04 to 18.04 breaks MongoDB

[LostNotFound]

Upgrading from 16.04 to 18.04 breaks existing mongoDB databases.

Pre update versions:
> lsb_release -rd
Description: Ubuntu 16.04.6 LTS
Release: 16.04

> apt-cache policy mongodb
mongodb:
  Installed: 1:2.6.10-0ubuntu1
  Candidate: 1:2.6.10-0ubuntu1
  Version table:
 *** 1:2.6.10-0ubuntu1 500
        500 http://no.archive.ubuntu.com/ubuntu xenial/universe amd64 Packages
        100 /var/lib/dpkg/status

Post upgrade versions:

mongodb:
  Installed: 1:3.6.3-0ubuntu1.1
  Candidate: 1:3.6.3-0ubuntu1.1
  Version table:
 *** 1:3.6.3-0ubuntu1.1 500
        500 http://no.archive.ubuntu.com/ubuntu bionic-updates/universe amd64 Packages
        100 /var/lib/dpkg/status
     1:3.6.3-0ubuntu1 500
        500 http://no.archive.ubuntu.com/ubuntu bionic/universe amd64 Packages

After upgrading the release, the existing database files fail to load with the error:
** IMPORTANT: UPGRADE PROBLEM: The data files need to be fully upgraded to version 3.4 before attempting an upgrade to 3.6; see http://dochub.mongodb.org/core/3.6-upgrade-fcv for more details.

To reproduce this I can use a fresh install of 16.04 fullyupdated, with a MongoDB running on it, and upgrade it to 18.04.

[LostNotFound (lostnotfound)]

I did a few more attempts, following these steps:
- Install 16.04
- apt update
- apt upgrade
- apt install mongodb
- Create simple database (using compass), insert a collection with a few entries
- do-release-upgrade
- MongoDB fails to start

Errors in the logs:
May 28 11:55:31 mongo systemd[1]: Started An object/document-oriented database.
May 28 11:55:35 mongo systemd[1]: mongodb.service: Main process exited, code=dumped, status=11/SEGV
May 28 11:55:35 mongo systemd[1]: mongodb.service: Failed with result 'core-dump'.

I attempted to start mongo manually:
> mongod --dbpath=/var/lib/mongodb
Which resulted in this output:
CONTROL [initandlisten] MongoDB starting : pid=1889 port=27017 dbpath=/var/lib/mongodb 64-bit host=mongo
CONTROL [initandlisten] db version v3.6.3
CONTROL [initandlisten] git version: 9586e557d54ef70f9ca4b43c26892cd55257e1a5
CONTROL [initandlisten] OpenSSL version: OpenSSL 1.1.1 11 Sep 2018
CONTROL [initandlisten] allocator: tcmalloc
CONTROL [initandlisten] modules: none
CONTROL [initandlisten] build environment:
CONTROL [initandlisten] distarch: x86_64
CONTROL [initandlisten] target_arch: x86_64
CONTROL [initandlisten] options: { storage: { dbPath: "/var/lib/mongodb" } }
- [initandlisten] Detected unclean shutdown - /var/lib/mongodb/mongod.lock is not empty.
- [initandlisten] Detected data files in /var/lib/mongodb created by the 'mmapv1' storage engine, so setting the active storage engine to 'mmapv1'.
JOURNAL [initandlisten] journal dir=/var/lib/mongodb/journal
JOURNAL [initandlisten] recover begin
JOURNAL [initandlisten] info no lsn file in journal/ directory
JOURNAL [initandlisten] recover lsn: 0
JOURNAL [initandlisten] recover /var/lib/mongodb/journal/j._0
JOURNAL [initandlisten] recover cleaning up
JOURNAL [initandlisten] removeJournalFiles
JOURNAL [initandlisten] old journal file will be removed: /var/lib/mongodb/journal/j._0
JOURNAL [initandlisten] recover done
JOURNAL [initandlisten] preallocating a journal file /var/lib/mongodb/journal/prealloc.0
JOURNAL [durability] Durability thread started
JOURNAL [journal writer] Journal writer thread started
CONTROL [initandlisten]
CONTROL [initandlisten] ** WARNING: Access control is not enabled for the database.
CONTROL [initandlisten] ** Read and write access to data and configuration is unrestricted.
CONTROL [initandlisten] ** WARNING: You are running this process as the root user, which is not recommended.
CONTROL [initandlisten]
CONTROL [initandlisten] ** WARNING: This server is bound to localhost.
CONTROL [initandlisten] ** Remote systems will be unable to connect to this server.
CONTROL [initandlisten] ** Start the server with --bind_ip <address> to specify which IP
CONTROL [initandlisten] ** addresses it should serve responses from, or with --bind_ip_all to
CONTROL [initandlisten] ** bind to all interfaces. If this behavior is desired, start the
CONTROL [initandlisten] ** server with --bind_ip 127.0.0.1 to disable this warning.
CONTROL [initandlisten]
INDEX [initandlisten] error: hashtable namespace index max chain reached:1335
- [initandlisten] In...

[LostNotFound (lostnotfound)]

If all files in /var/lib/mongodb is removed, mongo will start using:
sudo -u mongodb mongod --dbpath /var/lib/mongodb --smallfiles --storageEngine mmapv1

If the old db files are present, the segmentation fault occurs:

sudo -u mongodb mongod --dbpath /var/lib/mongodb --smallfiles --storageEngine mmapv1

I INDEX [initandlisten] error: hashtable namespace index max chain reached:1335
F - [initandlisten] Invalid access at address: 0
F - [initandlisten] Got signal: 11 (Segmentation fault).

[LostNotFound (lostnotfound)]

Does anyone have any input or opinion on this? Is this the expected behaviour and result?