When merging or renaming tags and topics, the existing filters and trends stop getting the existing values from them. What you will see in this case is a Filter or a Trend with 0 Results.
Fixing a broken Trend
To fix a broke Trend, first, you need to go to the Trends Page; next, find the broken trend and click on the Burger Menu on its right.
Click "Edit Trend", and change the topic or tag to the new one from the dropdown menu.
Click save and your Trend will start calculating the data right away.
Fixing a broken Filter
First, go to the page where you have the broken Filter. In the example below, we are using the Feedback Page. Click on the broken filter first.
Next, open the existing filters of it cli clicking on "Filtered".
Replace the broken topic with the correct one from the dropdown and click Apply.
Click on Save Filter and in the pop-up leave the option "Save changes to the filter" and click Save again.
