After more than 3 years of flawless use the box has been switched yesterday with a new STB HSV2034TAT2-520.
I had to reduce sharpness from 75 to 35 in this new box.
PS:
Issue faced on earlier box:
Video stucking, black screen but with info bar visible.
Even after swapping the box issue recurred after few hours (so clearly my earlier STB was fine).
Today he opened the LNB and refixed the wire.
It seems to be working fine now.
Amount for box swap has not been deducted even today(don't know why)