I noticed that on some of my TYPO3 7.6 extensions an action seems to get called twice, for example a listAction. If I put a vardump or an echo there it gets outputted twice, however the template is shown correctly once. I cannot discover any error in the code. The weird thing is on another site it does not happen with the same extension.
What could be the reason for this and how can I debug this?
Maybe you are using page.10.variables? Check my answer here what is the best usage of typoscript in fluid templates?