Lightroom web gallery : ordering problems

It's possible that you're not fully understanding how the Display tab is designed to work. At the basic level, it's intended as a means to allow the user to set the order in which the images in the specific album will be displayed when viewed by other people using the Shared Album feature. The display order is always going to be whatever has been set as the "Custom Order", and that custom order can be set by drag and drop in any of the client apps in the user's cloud ecosystem (including using the Display tab in LrWeb). However, via that Display tab in the LrWeb app, the user can do a few other things that can't be done in any of the other client aps: you can add dividers/headers/sub-headers/text to add interest and information to the shared alsbum for the viewers, and you can also "reset" the custom order using the option at the bottom of the Display tab's settings box.

So, you obviously understand how to add sections and text, but you need to realise that selecting one of those order options only does a point-in-time reset of the current custom/display order into whatever option order you have set. It does NOT change the "sort order" for all new images subsequently added to the album, it just changes the current "custom order".....so any images added to the album after resetting the order will only appear either at the beginning or the end of the album when viewed in the Display tab. Furthermore, resetting the order after you've added text will cause any added text to be removed, though you should receive this warning about that:

The way I work when adding text segments in the Display tab is to broadly get the album contents together (I do the editing before this). If I'm happy to use one of the standard sort orders, e.g. Capture Date, I'll reset the order as appropriate using the control on the Display tab settings, but if I want to use a specific custom order I'll use drag and drop in the Display tab to get them into the order I want (though you can of course get them into the preferred custom order using any other Lightroom app). Then I'll add the section dividers, headings, text etc. If, after setting everything up, I realise there are some additional images I want to add to the album, I'll add them then open up the album's Display tab, locate the added images (easy enough to do) and then drag and drop them into the position that I want them displayed in. Resetting the custom order is a bad idea in this circumstance.

Hope that helps.