When multiple A/B tests are running on the same page simultaneously, a visitor will become part of all the tests when he lands on the URL. However, we do not recommend you to set up changes on the same element in multiple tests. When multiple changes are being tested on the same element simultaneously, VWO will have two (or more) conflicting operations applied on the same element. User information will be recorded for different goals and might skew the test results. Running multiple tests on the same element can also cause conflicts in the applied changes on the live site.
As long as you are running multiple A/B tests to test different elements in each test then there should not be any issues. However, the results might not be statistically correct.
For example, test #1, variation A will display results according to what happens if you deploy variation A if test #2 continues forever. Similarly, data from test #2 will display results according to what happens if test #1 continues forever. A multivariate test might be more useful in this case.
Multiple Split URL test on the same control URL
Running multiple split URL tests on the same control URL simultaneously will cause conflicts as each test will redirect visitors to different variation URLs at the same time. When the same user is being redirected to different variation URLs, the user data may be recorded for multiple scenarios and result in skewed reports.