Hi,
On your second URL I see a white page with the text "Error". That text doesn't come from the sitemap plugin we provide on our website.
So I'm not sure what is going on.
First, a simple check: if you disable that HikaShop map plugin via the Joomla plugins manager, do you still have the error ? If no, then the issue is likely in the plugin. If yes, then it's likely not linked to the plugin.
Next, you can activate the "error reporting" and "debug" settings of the joomla configuration page and check that XML sitemap page again. It should hopefully display an error message with more information so that we can understand what's going on.