First, I know that all effects are cleared when leaving the End, but this is not about that. When traveling from the Overworld to the Nether and vice versa (as well as from the Overworld to the End), the Regeneration and Resistance effects stop working. They are still active effects in the UI, but the player (in this case, me) takes normal damage and regenerates at the normal rate. As a temporary solution, I've had to use command blocks in the Nether and the End to regain the effects, but it is still inconvenient. The Regeneration and Resistance effects were each applied using the following commands:

/effect give @p minecraft:regeneration 1000000 255
/effect give @p minecraft:resistance 1000000 255