Browser and app
Try another browser and check whether the behavior occurs in more than one application. Disable macros, button remapping and app-specific shortcuts.
Troubleshooting guide
Mouse double-clicking: what to check first
A browser observation is a useful clue, not an electrical diagnosis. Change one factor at a time, then repeat the double click test.
Connection
Check charging, battery level, receiver placement and USB port. Wireless interference can change input behavior.
Computer
When possible, test on another computer. Record what changed so a second round remains comparable.
Avoid concluding that a switch is defective from a single web test. A repair or replacement decision should use repeatable observations across environments.