Why the Oreo upgrade knocked my phone back to 3G?

[Android Central Question]

I have an unlocked Samsung Note 8 (on Straight Talk's Verizon service). Did the Oreo upgrade using Samsung Smart Switch. As soon as it finished, my 4G LTE disappeared and 3G appeared. Before the upgrade, I was getting 3 to 4 bars of service, now it shows 1 bar, sometimes none. Then 1x pops up frequently. Texting is slow and so is web browsing. Did a hard reset twice and now 3G stays up most of the time with 1 bar of signal. Samsung says it is a carrier issue and not on their end. I spoke to a guy who was in cellular sales and he said it may need a new SIM card from Straight Talk, so I ordered one. I can make calls and text. My phone test app says phone and data is 2G on unknown CDMA carrier. Anyone have an idea on what is going on?

 

[jlangner]

Do you have another phone you can pop sim into to check if carrier? Or a friend that uses Straight that can come over to compare?

 

[MarkNC]

Do you have another phone you can pop sim into to check if carrier? Or a friend that uses Straight that can come over to compare?

Unfortunately, no. Straight Talk said I would need a new SIM card and they would send one. Well I know how that works (I like the service, but they are sloooooow) so I picked up a $45 activation kit that includes a new SIM and monthly service card.

Called them up again, transferred the number to the new SIM, put it in the phone and WHAM, back to 4G service. Texts and browsing back where it was before the OREO upgrade. Also getting 3 and 4 bars on the meter at the top, 95 to 101 dBm signal strength.

Wonder why the upgrade caused havoc with the SIM? I hear a lot of Sprint customers are having issues with it too.