Grav update in admin panel is not working for me

At Dashboard page my installation tells me that a new update (1.1.14) is available (current version is 1.1.12).
After i clicked on displayed update button it tells me that new version is installed.
Seconds later it tells me again about that new update.

I tried cleaning cache several times and that behaviour did not changed at all.
The manual update has been not possible because i have not been able to find update packages that are described in "Download the Update Package from our Downloads section. It is important to download the update package and not the core package."
What can i do to get the automatic update working again?
It seems that changing from curl to fopen is getting the update back to work