It's been more than 2+ years that i have been using S8+ for my daily work.
It is still a great phone.

But, since last couple of months, my friends and clients keep complaining about the phone, that;
कति फोन गरे नेटवर्क लाग्दैन तपाइको।

If the caller is a friend, they can be answered. If it's a client, then the "फोन नलाग्ने" creates issue.
So,
I exchanged my SIM with another phone to see, if the S8+ has antenna issues
I also went to the Nepal Telecome Office to check my SIM - He reset all my default subscriptions and then the operator SIM chip is fine. He even called the number, the phone ranged many times.

So it is like, this time it's fine, and after few hours or few days, same "NETWORK" issue.
It was harassing, to restart phone every time or so.
I used "Device Care" option to optimize Storage and Memory. A lot of time.
I googled many times, and few results tricks didn't work.

How did I FIX it?

Simply, I copied all the image, voice, and video files into the laptop and erased all the document and multimedia files from the Memory Card as well as from the default Storage.

Then for couple of days, I put "Auto Restart" on. It worked.
Since then, until Now, i have no such complaints from my friends or colleagues or clients.

Sometimes I feel like my cellphone is so LITE to carry. Cause i deleted havy MBs and GB's of multimedia files out of it.

TRY and let me know if it works for you too.