Thanks @Mod-JakeM. Here’s some screenshots before 4pm PST and after. Spoiler, the Today volume bars disappeared at 4pm.
I also found another oddity, when volume is set to Today, the low of the volume bars ends on the low of the 3pm session but the High of the volume bars ends at the High of the day back to 12am PST.
On a hunch, I did a screen recording right before 4pm. And it shows the Today bars disappearing at 4pm. I can send it to you or post it to Youtube. Thanks for your help.
Before 4pm. Today and Yesterday volume bars visible.
Before 4pm. Low of Today volume bars begins at 3pm session low, not full day like the High bars extend to.
Before 4pm. Shows the High of the full day and volume bars extending to the High.
Before 4pm. Same phenomenon on the DOM.
After 4pm. Today volume bars are now gone.
After 4pm. Yesterday volume bars still show previous calendar day. I imagine it will change at midnight.
After 4pm PST. When Today is selected, neither Today nor Yesterday bars are visible.