If you are talking about using the simulator and it not taking your SFDCOAuthLoginHost value, take a look at this GitHub issue. It looks like the simulator isn't picking up the value correctly, but if you hook up your actual device it works fine. A bit inconvenient to develop with, but sounds like your only option.
We have discovered a build issue and are correcting the MobilePush SDK iOS version and will be releasing a v6.3.6 as soon as possible.
Please check our main docs page at https://salesforce-marketingcloud.github.io/MarketingCloudSDK-iOS/ for updates.
The error is CCKeyDerivationPBKDF Failure. ETPush's call to CCKeyDerivationPBKDF failed and the SDK either did not properly handle the error, or chose to crash instead of continuing in an inconsistent state.
The docs give us some reasons why CCKeyDerivationPBKDF may fail:
kCCParamError can result from bad values for the password, salt,
and unwrapped key ...