Since Matomo 4.2, Matomo creates a new visit as soon as a visit had 10000 actions within the same visit. So when action 10001 is tracked, a new visit will be created and all future actions will be tracked into this visit. This is to make sure Matomo stays fast as a visit with too many actions can slow down Matomo and can put a significant load onto the database.

You can change this behaviour by adjusting the config/config.ini.php file. For example to create a visit only after 50000 actions add the following lines to your config file:

[Tracker]
create_new_visit_after_x_actions = 100000

If the category [Tracker] already exists in your config file, don’t add this line again. To never create a new visit because of too many actions set 0.

[Tracker]
create_new_visit_after_x_actions = 0

You only need to change this setting if it’s normal for your site or app to have this many actions within one visit.

Note: You can also configure this setting on a per site basis.