I am also seeing the same errors. There appears to be a few places online where others are also seeing the errors. I’ve reverted to using 5.4.4 for now until there is more info. I need the engine to compile without problems and also nightly builds.
(tried the suggestion here but either I’ve applied the fix wrongly or its not working).
AUR (en) - unreal-engine ( See KarthikJay comment)
I am not at all an expert in building unreal but I wonder if the ubasessionserver might be the issue. All the thrown errors do not have (ubs disabled) next to them.
Post here how to turn the session server off - though I’ve not yet tried this. Might try overnight.