Wifi connectivity has been an issue ever since I bought my Nokia 3 at the end of Sept 2017. Bluetooth was similarly affected, but to a lesser extent than Wifi.
I initially thought there was something wrong with my phone hardware and had it replaced bu the issue has persisted.
What works for me is to turn flight mode on and off rather than turn the whole phone on and off. Even then I need to do this several times a day, certainly more than 3 or 4 times.
Something I found out was that on booting into recovery mode and doing a system partition check, several files are reported as missing, corrupted, or replaced. This was the case on both my phones and points to extremely shoddy quality control on Nokia's part.
I've been really disappointed with my purchase of this phone. I bought it to get an indication of how good the new Nokia phones are and was going to upgrade to the Nokia 8 (or 9 if it ever sees the light of day) but having been burnt by the Nokia 3, I've decided to give Nokia a wide berth. As far as I'm concerned, HMD Global is all all talk, no substance.