Always upgrade to the latest stable revision of your release series.
MongoDB versioning has the form
X.Y refers to either a release series or development series and
Z refers to the revision/patch number.
X.Yrefers to a release series; for example,
3.6release series and
4.0release series. Release series are stable and suitable for production.
X.Yrefers to a development series; for example,
4.1development series and
4.3development series. Development series are for testing only and not for production.
For example, in MongoDB version
3.6 refers to the release series and
.14 refers to the revision.
Changes in the release series (e.g.
3.6) generally mark the introduction of new features that may break backwards compatibility.
Changes to the revision number (e.g.
3.6.14) generally mark the release of bug fixes and backwards-compatible changes.