Platform, device version and operating system
What you were expecting to happen, and what actually happened
After starting a delve event (=spending a delve sigil), the difficulty setting from explore/quest battles is reset to normal. I expect the delve not to influence the difficulty setting.
How often does this happen? When did it begin happening?
Steps to make it happen again
Play an explore game on difficulty warlord 4.
Switch to delve event and spend a delve sigil to start a new delve.
Switch back to explore and check your difficulty setting. It is reset to normal