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V11 error in reports

Traceback (most recent call last):
File “/home/sanath/frappe-bench/apps/frappe/frappe/desk/query_report.py”, line 264, in get_prepared_report_result
data = json.loads(uncompressed_content)
File “/usr/lib/python3.5/json/init.py”, line 312, in loads
s.class.name))
TypeError: the JSON object must be str, not ‘bytes’

This is cimming in V 11.71

have you made any changes in query_report.py file?
or just run

bench update --reset

Remember, incase if you made any changes in core that will reset to the current branch.