Having Same Issue
April 26th 2021 Time 2:22am EST 
PC Specs:
CPU: Ryzen 7 3700X 4.3Ghz
Mobo: Asrock B550 Phantom Gaming ITX
RAM: G.Skill Trident Z Neo 32 GB DDR4-3600Mhz CL16-19-19-39 1.35V
GPU: Gigabyte Windforce OC 3X 8G 2070 Super
Drives: Samsung 970 Evo 1TB M.2-2280 NVME
Edit: Disabled All Addons Besides Guides Addon and still Presumes
Keep up The Great Work Dugi and Dev Team! will always prefer these over Zygor’s and any other Guide addon/3rd party websites
and can’t wait to relive TBC / wrath with this addon again like back then!
Installed a Debug tool called Swatter [Lib] that comes with Auctioneer to get detailed Errors 
Tried even copying the Libstat file and even the folder from the retail version I own to the classic one didn’t do nothing just made the addon disappear entirely off the screen and used the /dugi chat commands to see about messing with it and just went back to the error above went I did /dugi on
Fixed Mine Now
Not Sure if this is why it’s fixed but I went into the Addon Folder for the Guide and deleted The GearAdvisor LUA Files and then reloaded UI typed /dugi on and boom everythings back on
Hope that Helps for everyone else with the issue