This Asset store package is using Texture2D.EncodeToPNG() in one of their DLLs.
After 19.1, this error keeps appearing when running their example scenes:

MissingMethodException: byte[] UnityEngine.Texture2D.EncodeToPNG()
Adinmo.AdinmoDownloader+<DownloadImage>d__13.MoveNext () (at <d5fbebea95934262acb0d16ffb8cc7c5>:0)
UnityEngine.SetupCoroutine.InvokeMoveNext (System.Collections.IEnumerator enumerator, System.IntPtr returnValueAddress) (at C:/buildslave/unity/build/Runtime/Export/Scripting/Coroutines.cs:17)

This does not occur in 18.3. Also, I have tried making a very simple projects that uses Texture2D.EncodeToPNG() in a c# script, and that seems to work, so it might be related with calling the function from the DLL...

To repro:
- download this project
- play the ExampleDialogue scene

Reproducible in 2019.1.0f1, 2019.2.0b3 , 2019.3.0a3
Cannont repro in 2018.3.5f1, 2019.1.0b10