Need a Photo Gallery Solution

Hello! I am looking for a solution to a problem we dealt with last year and are looking to avoid this year. We are a production company that tours artists across the country and on a given tour, we may have 30-40 stops on which each city has a meet & greet, photos we upload for access to the customer. There are usually about 200 images on average and this process is pretty continuous, in the 24-48 hour window of a show the upload has to be completed. By the time one is uploaded, we've usually completed the next, and so on.

Last year we simply uploaded everything to a gallery but the following problems presented themselves almost every single time:

* It was incredibly slow. Even with scaled down images. We have to provide hi res images so ideally we don't scale them down a whole lot. But that said, uploading them to Google Drive or Facebook was always super fast. Squarespace, no matter what internet we were on or the file size or anything, was horridly slow at this process.
* The uploader would just randomly fail in the middle of an upload and go to an error screen. You couldn't refresh or back out, you had to close the browser and open it again (on different browsers and devices consistently). Then, you had to go back and determine where the upload cut off, which is difficult when every photo is the same except the person standing next to the artist.
* Sometimes everything would seem to work fine, but then we'd get emails saying their photos aren't there. The uploader would just skip random ones. So then we started uploading 20 at a time each night, which was tedious and even slower.

So I don't even think using Squarespace's albums is an option for this type of situation (which is very odd considering they market themselves to photographers). Anyway,

* I'm into a third-party service if it makes sense and isn't costly. 
* Whatever the solution, we need multiple contributors to be able to upload to it
* I saw options to embed Facebook albums but I don't want to be beholden to FB's random site changes and would rather keep it "branded" so to speak
* Sites like Flickr and linking people out to Pixie Set or whatever aren't great, we don't want to link out, we want it embedded on the site

Any advice? Or is there a way to make the Squarespace albums behave better?

Thanks a bunch!