When upgrading from Unity 2018.4 to Unity 2019.4, please make sure that you also upgrade the TMP package to the corresponding version of the package for Unity 2019.4 before making any changes to your project. If you were using version 1.5.x of the TMP package in Unity 2018.4, you will need to install the corresponding version 2.1.x via the Package Manager in Unity 2019.4. This is especially important as the older version 2.0.1 of the TMP package will be installed by default in 2019.4. As such, if you were using version 1.5.x of the TMP package in Unity 2018.4, this will result in a downgrade of the TMP package resulting in potential issues including incorrect text alignment. Provided you do not make any changes to scenes, prefabs and assets before updating to the corresponding version of the TMP package for 20194.4, everything should be fine. You may need to re-open a previously loaded scene but that's about it.