wordpress editor removes format

i am having problems with one of my websites (self hosted). when i type in text in the wordpress editor it randomly removes formatting (line breaks especially). i already tried to solve this problem by disabling all plugins but it still remains. the weird thing is, that it sometimes works and sometimes not. which makes it even harder to find the problem.

i am using the latest wordpress version and quite a few plugins, but as i already said, i couldn't find a specific plugin that causes the problem.

any help is appreciated. i could also provide access to the page if necessary.

you can find the website here: http://ift.tt/1OYzx2a

via Chebli Mohamed