I have reported to SpeedTest CLI support too. However, I am not entirely convinced this just Ookla issue. Do we really believe Ookla tests their CLI on all possible routers?
I can easily imagine a situation this is purely AX88U issue.
Key question is
why SpeedTest CLI does not distribute workload on four AX88U CPUs?
What is so different about AX88U hardware/software? Presumably same CLI source code once compiled and deployed behaves differently on AC86U and on Windows machine as opposed to AX88U. On the first two it distributes load on many processors resulting in 850Mbs speeds. Perhaps
@RMerlin has some suggestions...
As it stands spdMerlin / Ookla CLI is pretty useless to me and I have deleted it from my router.