I just recently ran into this problem, whenever I use Google Search, the "safe search" option is always on, and I can not manually turn it off, I have already tried to log on different google account, using different browsers on different devices (laptop, desktop, tablet, mobile phone) the outcome are the same, for example every time I uncheck the "turn on safe search" box on the google search setting page and apply the "change", the safe search filter will back on automatically immediately.
I have also noticed there are lots of websites have been blocked suddenly, or no longer accessible from my home, not sure if it is related to google safe search issue I'm having right now but I think any VPN related websites are blocked from me at home atm, i.e. https://www.expressvpn.com .
so I did some research online, apparently there were a lot of ppl that had the same issues or used to, and according to one of the google employees on this thread (https://productforums.google.com/forum/#!topic/websearch/QKVKcDhCdWA), that the issue(SafeSearch) is ISP related, and ppls saying I need to contact with my ISP to resolve this. So i just want to know if this is true, or if anyone is having the same issue right now, thanks in advance.