It sounds like you’ve done a through job in going after the usual suspects.
From the video, it seems like there might be a feeding issue, especially when the video shows printer makes long and fast head movements. If you’ve accumulated over 1500 hours of printing, even though it’s not a high amount, wear and tear on the filament travel mechanism could be causing this problem.
You mentioned cleaning the extruder, but did you consider replacing the extruder gear? Have you checked the Bowden tube and considered replacing it? I also noticed in the video that you were using a Sunlu dryer box for the filament. Have you tried a direct spool feed from the printer’s spool holder? I mention these things because if the problem is related to feeding, eliminated any possible points of friction along the feed path and ensuring a strong grip on the extruder gear would help rule out feeding issues as a potential cause.
A last ditch effort if feed might be an issue is to try clipping on a filament filter.
https://www.printables.com/search/all?q=filament%20filter
Some people have used a small amount of olive oil to lubricate the Bowden tube. Stefan from CNC Kitchen has made two videos on this topic. One from six years ago supports this approach, while another, more recent one disapproves because it shows that the oil can affect the filament’s quality and adhesion. If you’re making structural parts, this method isn’t advisable. However, if you’re focused on crafting parts where appearance matters most, it might be worth considering.
Consider Stefan’s advice with caution. He mainly focuses on creating stronger parts and testing their durability in his videos. While his content is informative, your specific use-case might differ from his.
Here’s a video from Matterhackers that goes into the hows and whys. Try to not judge the presenter, he’s goofy AF but his point is one to consider.
