I have the same issue with my S9+. I bought it 3 months ago but the problem started this week. We have a 2.4/5g router and idk what to do. I tried to change to static but problem still remains. Bluetooth is off as well. HELP.
I've had exactly the same in the last week on my S9, if I have bluetooth on hardly anything then fine if I turn it off. If I turn it on and put it next to my wifes S8 which works fine with BT on, it messes her wifi up as well!
I need to have both on for car handsfree/wifi zone and connection to smart watch so it's pretty useless at the moment.
I habe been on Twitter with them today and yesterday but they're just saying they don't know what it is.
Another thing that might help, go into your router settings and set channel to 11. Some countries use different channel widths on their devices so if yours is different that may be the cause as I think the s9+ is American. It's possible that Bluetooth is using a channel to interfere. I'm only half technical so I may be talking out my ass
I was experiencing the speed issue as well, and I solved it by tweaking the transmission power on my access point. Both 2.4 and 5 GHz bands were set to automatic for power level, and I manually set the transmission power to medium for both (Unifi AP-AC-PRO, but similar settings probably exist for most access points). As soon as I changed the power, my S9+ defaulted to the 5 Ghz band, and my network speed increased to 400 Mbps. Perhaps the phone automatically chooses the band with the loudest volume and my 2.4 band was more powerful than the 5 (the phone chooses transmission volume over netword speed).
I can also verify that turning off Bluetooth fixes slowdowns almost immediately on my S9+ (Verizon)
I've had Similar issues with Raspberry Pi 3b boards, amd the consensus was a module in the Kernel was to blame.
Either way, Samsung should hop on the dev team to try and sort this out. It's one of "those" annoyances that tends to create bigger problems for the company as a whole, because MOST users won't even look THIS far, they just abandon the brand.
I spoke to samsung today. They said if you log an error through the Samsung app once they get enough they can start to create a fix.
Go to support then error log.
Can you be more specific with which Samsung app? In settings>help Samsung has a redirect to a webpage for help, but no error logging; and in settings>developer options there is an option to send data, which I have done, but there is no field to specify a problem.
Where did you submit your feedback?