Newest version of python package is not available

I'm using Sonatype Nexus Repository ManagerOSS 3.15.2-01 upgraded some time ago from 2.xy (don't remember exact value, but if required I can check it) version.

I have hosted pypi repository with few proprietary python packages and few versions for each package.

Precondition

1. on pypi repository package xyz is available in the following versions:
   1. 1.2.0,
   2. 1.3.0,
   3. 1.4.0.

Scenario

1. package xyz in version 1.5.0 is uploaded to the repo

Error 

1. command pip install xyz will install xyz in version 1.4.0,
2. command pip install xyz==1.5.0 returns

Could not find a version that satisfies the requirement xyz==1.5.0

Expected behavior

It should be possible to install package xyz in 1.5.0 version.

Additional observations

In the repository browser I see new "file" simple/ with list of the already downloaded from this repo python packages. There is package xyz listed with link .../simple/xyz.

When I click this list all "outdated" versions (1.2.0, 1.3.0, 1.4.0) are listed but the latest one 1.5.0 is missing.

Command

pip search xyz

is able to detect

LATEST: 1.5.0

version, but I can't install it.

In the previous version on Nexus such configuration was working without any problems.

Is there some new (new for me, because of upgrade from Nexus 2.* to 3.15.2) mechanism added to Nexus to publish new python packages? I have read PyPi repository documentation but unfortunetlly there is nothing which helped me to find a root cause of my problem.