I had this problem and ServiceNow provided me with this solution:
It has been identified as a known error and a PRB - PRB1828730 has been created for the same.
PRB1828730 - Sub - flow/Flow shows as 'Content cannot be found Your flow cannot be found. Flow sys_id:n' The flow exists in the system but we re not able to open it.
The PRB is in testing state now and is targeted to be fixed in Yokohama Version of servicenow.
The workaround for this PRB is documented as follows:
1.Delete the 'Content cannot be found' popup from the UI. (Right Click - Inspect - Go to Elements - find '<div class="ReactModalPortal"> ' and delete. This will remove the pop - up of 'Content cannot be found Your flow cannot be found. Flow sys_id:n'.
2. Go to 'sources' tab, Hit 'Command + P', Type 'Designer Bundle', choose the first file.
3. Control F and search 'actionsMap[id].warnings' and put a break point at this line
4. Now refresh the flow page again
5. Go to console, search 'warningforinput'and select the file and hit enter
6. This will give the step at which the error is (gives the unavailable/wrongly used catalog variable) - this says that there is an issue with this catalog variable (it can be a data - pill or inline script as well)
7. Keep on hitting on play button so that the next errored catalog variable is seen.
8. Go to catalog item from where this catalog variable is coming from and check if this is available.
For me, it was because I had modified a Catalogue Variable's name, and that Catalogue Variable was being used as a Data pill in one of the actions.
I had to delete the Data pill then re-add the Data pill to fix it.
