Thank you Brajesh,
I have tried with latin characters and with less than 50 and also without a subject (to not be shown or required), but the problem remains.
I apologize for giving you a headache over this issue. I hope we can resolve it somehow.
Please, mind that the reported object (eg. an activity) is added to the queue but there are no options there to do something with it (eg. approve or suspend, as I understand it should be) other than visit the reported item or delete the report. Another thing I have noticed, is that mass deletion (checking all the boxes at once) is not an available option in the queue.