GeneratePendingTransforms stuck every time I get a stuck GeneratePendingTransforms task over and over again. In the first place, I don't know why any transforms are getting created at that point. By now, almost every image transform for every image on the site must have been create once. And it seems like those generations happen on the weirdest moments. It can't be the images of a freshly posted entry that had to be created, because there's always +300 steps in the tasks (and there are 5 images at most on a new entry).

Anyway. It seems that those tasks also get stuck every time. I don't know why they get stuck. And yes, I know you can change the status to pending. But I can't keep doing this 10 times a day. The craft log doesn't give me much more information. Right now I have a GeneratePendingTransforms task that is stuck at step 333 from 341. And this is the latest info in the craft log file:



2016-10-08 21:55:00

Level   error
Category    exception.Craft\HttpException.404
Message Craft\HttpException in /srv/users/ijnluser/apps/ijnl/craft/app/controllers/TemplatesController.php:59



I don't know if stuck tasks also prevent the execution of pending tasks? But I also noticed cached items don't get cleared at all, and I have to clear them manually. Could this be because they are waiting to run, after the stuck task is done?
I think to solve your issue we're going to need a bit more of information. A couple of things you can try:


set a higher max execution time. I think normally the max execution time is 120 sec. and this sometimes blocks other transforms
try using the craft task manager plugin to remove any tasks that get stuck. 
try reindexing the images, remove all the cached items, check your folder permissions


That being said, I stopped using the image transforms Craft provides out of the box and started using Imager. Imager provides a handy way to do transforms in your template. Works like a charm and lots of handy options.