please, one thing after the other 
The images are not flipped, they are acquired in ascending mode, the data will be adjusted after terrain correction: S1 image opens upside down
No change of URL needed, please test the SRTM 1Sec (Auto Download) instead and make sure that SNAP can pass your firewall, please see here: S-1 Thermal Noise Removal
Again, what output format did you select for the subset? Does the image look alright after subsetting?