I am using version 1.14.2-forge-26.0.16. When clicking on the Minecraft Realms button from the title screen, the client immediately crashes and throws an exception stating:
The game crashed whilst mouseclicked event handler | Error: java.lang.VerifyError: Bad type on operand stack
I have included the debug.log output of the session when that particular crash occurred.
This bug does not occur on a clean installation of vanilla 1.14.2. I did make a separate clean installation of Forge 26.0.16 onto a different directory, and I was able to reproduce the same error. I have also used a different computer with a clean installation of Forge and with profile settings set to default (e.g. using the default JVM arguments, bundled Java runtime), and I managed to reproduce the bug successfully (see spoiler below).
I am looking forward to any updates regarding with this issue!