I'm getting the same error as the https://tracker.moodle.org/browse/MDL-67140 but with moodle 3.9.1
However line numbers differ -
Missing required key in single structure: year
Error code: invalidparameter
* line 349 of /lib/externallib.php: invalid_parameter_exception thrown
* line 240 of /lib/externallib.php: call to external_api::validate_parameters()
* line 81 of /lib/ajax/service.php: call to external_api::call_external_function()
**I think** it is a problem with my theme as it doesn't occur with Boost but as it's a child of Boost so can anyone suggest where I might look please?