I don't think there is any way to sort by title without a plugin or script.
You can sort a collection by title using a free script I wrote:
'Order Photos in Collection' ("Title.." preset)
There are other options if you don't actually need sorting so much as.. - please let me/us know if the script does not suffice.
PS - the sort options in Lr are indeed lean, and there have been some requests to fatten it up, you may look here:
I think you are looking for the sorting options in the wrong place.
Once you have uploaded the files to 500px the sort order are most likely controlled by gallery options at 500px.
Or at least that is how the LR plugin works with Zenfolio:
Zenfolio allows me to choose either upload order, by date, title and manual for sorting in their galleries. I would look at your sort options within the galleries at 500px to correct your sort order problems. Other than the 'upload order' choice changing a sort order within Lightroom does not change anything after they have been uploaded. I can change order online but LR plugin does not see the changes/care unless there is a move or deletion.
Thanks Rob, I will give this a try.
500px sorts them fine on their website. The 500px exporter uses the Title as the title on 500px, and 500px.com sorts by title by default. The problem is LR does not sort by title, so the photos appear in a different order when in LR vs on the web. This problem is solved if LR can sort by Title.
Rob I just tried your sorting script and it worked like a charm.... I wish I didn't know LR was scriptable. I have no interest in building a plugin, but scripting is fun... and time consuming.