Hi,
I was able to check your website with an access you provided previously (it's aurumsolis.info, right ?).
1. I am not able to reproduce the issue. I was on the configuration for half an hour now. I saved it several times, went to other pages, came back. It worked all the time.
2. I was able to add an image after several attempts. Most of the time I got a memory limit issue.
That's because of the way you configured HikaShop. You set a watermark of 2200*3000 px.
So the system is trying to apply it on the images each time you upload one. So it has to load the complete image you're uploading in memory and do the same with the watermark and then have a third image being the combination of both and then yet another one for generating the thumbnail. All that requires a lot of memory, even more so that your watermark is really big.
With such a big watermark, just loading the watermark in memory eats up between 30 and 50 MB while your limit is at 64M.
Also, you're using a watermark with a white background and an opacity, no wonder that your images get blurry when you upload them and that you don't hit the memory limit.
So you'll have to do something about the memory limit and/or the watermark if you want it to work properly. It's not something which can be fixed in the code of HikaShop.