Hi @MaghSamana, if you were to perform the same actions as this user, would you see the same performance metrics show up in Matomo (in other words, is the problem reliably reproducible)? Can you see what browser, os, internet provider the specific user is using?

The visitor used Chrome 91.0 and Windows 10 (and 1366x768). I haven't added internet provider tracking.

I will try to reproduce this tonight, and get back to you.

After various tests, and with various browsers, the problem of extremely high DOM is certainly tied to Chrome browser v. 91.0.

Both in my tests, and in the visits with excessive DOM (from 20 secs, reaching as high as 80secs the more downloads there are), it was always this particular browser version.

Browsers like Safari, Edge, do not reproduce this. I got partial reproduction with Firefox 89 - high DOM but not as much (10-12secs at most).

Hi @MaghSamana, thanks for testing this! Would you be able to reproduce this and collect the network requests made to your matomo.php instance, then share them here? Or if you're comfortable sharing the website this is happening on, we can take a closer look (email me at dizzy@innocraft.com if so).

I keep seeing these bizarre metrics again and again. Anyway, I sent you an email, and let's see what could be the issue here.

Based on communication w/ @MaghSamana, this is definitely some kind of bug, though I'm still not sure what the cause is. I'll keep looking.

Finding the cause of the issue is proving to be rather difficult. It seems to be due to a single visitor that downloads PDF documents.

The quickest way to solve this would be to add segments for page performance dimensions. This would allow users to ignore values that are greater than a threshold, or find visits with abnormal values to figure out why they are like that. As it is now, it's extremely difficult to find this information, having to query the log tables directly.

👍 We'll look further into it once the issue is scheduled. We'll probably wait first to see if other users are having a similar issue. Possible it's an issue with that Chrome version. For the segments we have an issue here: #10202

And also created #17824

Another case for high DOM processing is:
Visitor opens multiple/all links on page in different tabs at once.

The browser processes like 20 page loads at once and the time for DOM processing really gets up. After the pages are loaded, the pages report their performance data to Matomo e.g.:

• 1 visit
• Total time on site: 50 seconds
• Page impressions total: 20
• DOM processing of each page: ~ 30 seconds

In this case we might try to somehow recognize this behaviour – and then flag this performance values or ignore them:

• When a page is loaded in a 'not actual visible' tab:
  Recognize via javascript?
• When multiple pages are loaded at the same time:
  Recognize server-side on report generation?