When switching from the editing tab to any other tab, all of the open timelines on my sequence window go away and the only one that remains is the one I'm currently viewing.
Export mode shows the current selection from Edit mode. Even though multiple Timelines are open while in Edit mode, only one Timeline may be in focus at a time. As such, the Timleline in focus is what shows in Export mode.
To have multiple Sequences while in Export mode, select more than one Sequence in the Project tab while still in Edit mode and then click over to Export mode.
When having multiple sources selected for Export mode, I find it helpful to immediately click "Send to Media Encoder" at the bottom right and continue in Adobe Media Encoder.
Yeah it is now really annoying that you confirmed it it is a feature.
Example:
I have 10 reels 1sequnce each in a project that I am currently editing. I am in the "Editing Workspace" when stitching the clips then I'll go next to the "Graphics or Captions Workspace" for the titles then suddenly only 1 sequence is open because I switch to another workspace, the biggest time waster here is I'll go open project panel & open the 9 other sequences again.
I'll switch again to the "Color Correction Workspace" then AGAIN only 1 sequence is open, I have to open another 9 again.
Then switch to "Effects Workspace" then only 1 sequence is only open.
You can duplicate my example & see how irritating it is.
Doing over and over a unreasonable clicks for a feature is a big NO.
Adobe please give a second look at this feature because it's not helping at all.