Looking at the syslog the cache devices were wiped, you can't just start the array multiple times while trying various configs, there should have been a red warning "data os this device will be deleted at array start" or similar for one or more devices, not even btrfs restore will work now since the superblocks were deleted, only option would be a file recovery util like UFS explorer, but not sure if it would work for this case, there's a trial if you want to give a shot.
There are several segfaults and btrfs checksum errors, which suggests a hardware issue, like RAM errors, start by reading this:
https://forums.unraid.net/topic/46802-faq-for-unraid-v6/?do=findComment&comment=819173
Any LSI with a SAS2008/2308/3008/3408 chipset in IT mode, e.g., 9201-8i, 9211-8i, 9207-8i, 9300-8i, 9400-8i, etc and clones, like the Dell H200/H310 and IBM M1015, these latter ones need to be crossflashed.
The errors are likely harmless, and if the new firmware doesn't fix them try with 16.00.01, which is the one most commonly used with those models and known to work without issues.
If you get those low speeds writing to cache and array (with or without turbo write) it suggest a problem outside Unraid, like network or source computer, see what you get running iperf test.
Since the extended test passed the disk is currently fine, and the pending sectors are "false positives", though it's never a good sign especially on a new disk.