I have that problem too (glad to know others do too. I was afraid it’s a problem on my side 
)
What I do is I upload one image at a time and save the episode after each upload. It takes forever (especially if you have more than 10 images) but it works. And if the site bombs out on you, you don’t have to start from the beginning again.
I also try to make my images as small as possible. That way they upload quicker and the chance of Webtoons freezing up on me is smaller.
What computer do you use btw? I’m on an iMac with the latest IOS. Maybe Webtoons has problems with that atm 
OH!!! I'll totally do that from now on, THANK YOU!!! It does sound super slow but is the best solution so far! Webtoons should add a "cancel" option to their uploading bar at least xD
I'm on a Macbook with the latest IOS too, do you think that's why we're having problems? :S I tried with different browsers and didn't work, but why should the IOS be such a problem in a web based app?? :S (I have no idea tbh, I hope it's not that orz).
Uff, with all the problems Webtoons has, they should at least have a working support center D:
I managed to update today after a couple of tries and someone suggested a way around it. Looks like we're stuck with this when it comes and goes :T
Sorry, english is not my mother tongue and I get confused some times D: But yes, you're totally right!!! I'll do that form now on! Thank you!!!
I am literally dealing with this problem right now and I have over 14000 subs so it's not a "small" comic issue. What I think and i'm hypothesising right now is that any image above 300kb automatically gets caught up in the system. So far if I downsize any image about 300 down to less than that all the images load up. Maybe try that!
EDIT: ok scratch that, after fiddling with file sizes for like 15 mins already. below 200kb is completely fine. uploads normal. 200-300 is iffy. you gotta have really good internet or be patient. 300kb just does load.
And I have relatively good internet. I have no problems with Tapas.io. this is frustrating
8 days later
Those who have problems uploading, is your comic drawn in black/white or colored?
I noticed that I don’t face the freezing issue when I upload colored images (banner and such), even if they are bigger than 300kb. But b/w images, even when small, tent to freeze.
Anyone else experiencing the same?
If my images are lower than 200kb I do a few at a time then save the episode draft before attempting the next lot. It is so laborious now. It's like webtoons wants creators to stop using it. 
18 days later
Hey guys, I just tried to uploaded my current episode and ended up playing around a bit.
In my case the problem is definitely the color.
My comic is black/white with tones and the site always chokes on them, even with tiny size (one was 80kb, for f’s sake! 
)
I overlapped a color layer on one of my panels and it uploaded it within an instant (although the colored version was twice as big as the b/w original which I couldn’t get up).
Same probably goes for text in b/w.
I bet they have a program which blocks certain images from uploading in order to prevent spam (dunno if something like this is possible since I have no idea about stuff like this 
)
Anyway, my current arc takes place during a Blackout, so I struggled through the upload with further edits..(took me forever, grrr). But with the following arc I will overlay all my comics with a colored gradient. If that’s the only way to get my stuff up there, so be it ...
If your comic is b/w too, add some color or an overlay. I’m not sure if that’s the resolution to the problem. It works in my case and is still a lot better than compressing your files to tiny size but crappy quality....
3 months later
Having the same issues.
I'm new to Webtoons and unable to upload my first comic. Last night the first page loaded, then the site froze. Since then I have been completely unable to load even a single image.
My troubleshooting (none has worked):
I have tried b/w vs color.
File size is under 100kb.
Used "save for web" in PS as well as regular save as. No difference.
Yes, all JPEG formats.
Tried wi-fi and alternatively a direct ethernet connection. Did not help.
I updated Flash.
I updated Safari.
Tried a full batch vs. one image at a time.
I absolutely CAN NOT get this website to do anything! I have submitted "feedback" but I'm not optimistic about a response. I see other users have uploaded hundreds of comics; I was really hoping to do the same over time, now I feel like I don't even want to use this site if it's that broken. Ugh.
1 month later
Hi, I was having the exact same problem! My first solution that (kinda) worked for me was lowering the quality of the images before exporting them. The obvious problem is that this made my webtoon look really low quality, and it wasn't as vibrant. Also, even after lowering the quality, the same images would sometimes not upload AGAIN which meant I would have to lower the quality even more.
BUT- there is a better solution. If you're using Safari, consider switching to a different explorer. I used Chrome and my files didn't freeze ONCE. There was no need for me to even reduce the quality of any of them. Please give it a try! I hope everything goes well 
1 month later
Well poop, it's happening to me now. I am trying to upload just one page. I select the file and the "uploading file" message pops up and that's where it ends. I can still scroll around, but the message stays at 0%. Same for the thumbnail. I tried to use Chrome and Firefox. I tried the same with older pics, that I uploaded to webtoons already (not that long ago actually). It's the same for these pictures. I tried to resized the picture, even though it already fit the size criteria. Updated flash, disabled adblock, even though it shouldn't be a problem...
Any more ideas what I can do? It is a little bit annoying to really try your best to meet your deadline for the release schedule only to be blocked on the finish line 
Hi I was having the same issue right now, and the way I solved was uploading the comic from https://upload.webtoons.com/en/259 instead of www.webtoons.com24, In my case was a crossdomain browser security issue, hope this helps.
