I know that problem... Solution = when you're In The game got to shop - currencies - free EP (it opens the browser and you're automatically logged into your hunted cow account and you won't get logged out on client).
I don't use steam but I know there is an eldevin forum on steam but I absolutely got no clue how to reach that or even post in there.
But interesting would be if that's a "common issue" cause in such a case it should get fixed.
She played Eldevin (steam verision!!!) from start, as we decided to get some free EP from the offers wall she coulnd´t log in anymore except with the browser version (interesting part steam / stand alone client didn´´t made a difference BUT with a virtual machine to emulate Windows she was able too log in via stand alone client also i have been able to login to her account with my Computer thats why i thought it might be a Mac issue but well it wasn´t). She noticed her achievements aren´t shown in steam anymore, she created a new steam account and linked her eldevin account with the new steam account and ... it works (don´t ask me why she was always using steam and after she used the offers wall it just didn´t worked anymore and if This happens to other ppl who found eldevin via steam i´m not surprised if those ppl quit the game after a few minutes cause they couldn´t Login anymore.... that´s something which should be tested and most probably known by the Support which didn´t helped and most probably got no clue if this is a common issue or not otherwise the Support could have helped i guess...).
regards
Purple Duke
edit:
btw sorry was too excited to be able to Play the game again with her that i didn´t really thought of giving the solution to the Forum ... my fault xD