Hi,
I would recommend editing the file libraries/src/Event/AbstractEvent.php and then, on line 223, add such code:
if(function_exists('hikashop_writeToLog')) {
hikashop_writeToLog(var_dump(debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS)));
}
Then, on one tab of your browser, open the HikaShop configuration page, and on another tab, reproduce the issue.
Once the the issue is reproduced, go to the tab with the HikaShop configuration, and under the Files area, open the "payment log file".
This will open a popup with debug information. The latest entry should contain the debug information added by this code modification. It will allow us and you to better understand why this is happening.