Hello Eva-Wiehl
Welcome to the Community Forum!
We have seen this issue for a few Activity Statements, and it seems that the cause of the issue is that while the Activity Statements are for 2018, they are getting created within the 2017 tax return.
To fix the issue - the first thing to do is make a note of which form type the Activity Statement is, and any figures you have in there (or you could print it out). From there, open the 2017 return, and go to Preparation > Delete Schedules. Select the specific Activity Statement, and then click on Delete.
You will then need to manually create the Activity Statement within 2018, using the form type from the one you just deleted. I've included a link to the Help page with instructions on how to create the Activity Statement manually, in case you're unsure:
Creating an Activity Statement
Hopefully that will solve the problem for you!
