@Paul, As you have basically the same hardware as the OP can we confirm a few things and eliminate things in common?
I have the same hardware but run things differently:
1. I have an Envoy and USB logger. I mostly run Cumulus with this connection, but every 15 days I stop Cumulus and run Weatherlink 6.0.5 for a while to keep the Weatherlink data up to date (logger interval is 10-minute which is about 17 days). When this runs with Weatherlink 6.0.5 it uploads to Weatherlink.com basic account
https://www.weatherlink.com/bulletin/a3a3c5e7-b8bd-4910-ba3a-f6ad6e1f09d12. I also have a Vue console with the WiFiLogger. Through WiFiLogger in Weatherlink PC mode it uploads to Weatherlink.com at 5-minute interval to that same Weatherlink.com account. However, this Weatherlink.com account is a basic account so the data is at 15 minute interval. I can view this data if I temporarily move my Pro subscription from my Weatherlink.com Weatherlink Live account
https://www.weatherlink.com/bulletin/13ce8169-7074-4187-98af-059ea4c354b0. My WiFiLogger is wireless/WiFi rather than ethernet, but ethernet connection is available.
At the same time as uploading to Weatherlink.com the WiFiLogger can be connected to a PC running another program, and I have that with CumulusMX. CumulusMX has a Disconnect setting to allow the WiFilogger to do all its non-Cumulus uploads. I believe, but have no experience with it, this is similar to settings in WeatherlinkIP to permit both uploads and connect with a PC.
When you say "WL IP mode" is that totally self contained without any PC connected or running? Which is how the Davis WLIP uploads.
I don't run it this way, but yes it would be without any PC connected.
"WL PC mode" So this would be via the connected/running PC with WeatherLinkPC open using a Device ID & Key obtained from Weatherlink.com and config'd under Setup>Weatherlink Network ?
Partly yes, in that instead connected/running PC with WeatherlinkPC and having this upload to Weatherlink.com, it is live WiFi connected/runs with CumulusMX and once a minute CumulusMX disconnects for WiFiLogger to do its uploads to Weatherlink.com and the other weather services.
It appears the OP's WiFilogger is updating Highs/Lows throughout the day but does not reset the Highs/Lows at midnight/day rollover? Correction if I have this wrong.
From checking WeatherRick2 weatherlink.com site the Today's Highs and Lows are correct and being updated that I have seen so far but that may be because Rick has been restarting his Weatherlink 6.0.5.
Can you confirm that your Highs/Lows reset at midnight? If so then the focus goes to the OP setup/config and/or other.
Sorry, as I run Weatherlink 6.0.5 for no more than an hour or so twice a month I can't confirm that.
My question to WeatherRick2 regarding how he uses his WiFiLogger is to see if his use is similar to mine as WLPC or if using as WLIP and if that may be the cause of his issue.
Enjoy,
Paul