1.18.3.2129 was released in December 2019.
Current versions are 1.23.5.4862 and 1.23.6.4863 (Plex Pass) [Reference].
The current releases contain fixes to improve the reliability of remote access (put in place in late 2020 IIRC).
Also, there is a problem with current Android / Android TV clients and old (1.18, etc) versions of Plex Media Server. The problem does not exist with current Plex Media Server releases.
If possible, update to a current release.
