Hello,
If you don't have any entry in the log, it seems there is no error to log for the plugin.
If you can reproduce the issue, please open the browser console ; the JavaScript will add the received content from the server if if can't process it correctly.
Sometimes it can be related to a system plugin which will add some content and makes the JSON invalid to decode.
If you don't have any error in your log, it'll be the only way to understand what is going on.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.