Invalid Session Please Try Restarting Minecraft - when attempting to log in to Realms

(This issue is in 1.12.2. The Affects Version option doesn't have 1.12.2 as an option.)
When I click the Minecraft Realms button, I am met with this error message: Invalid Session Please Try Restarting Minecraft
What I expected to happen was...:
I expected the issue would be resolved after restarting the game, logging out of the launcher, and rebooting my PC.
What actually happened was...:
The issue persists after doing the above mentioned "solutions".
Steps to Reproduce:
1. Click the "Minecraft Realms" button
2. Receive error message