Brave freezes when loading TXT file into NAS

I use Brave as my main browser and as such use it to access the web based UI for my Synology DS218+ NAS.

All works fine unless I go into the NAS control panel and look to load in a list of IP addresses I want to block. This list is updated regularly and at the moment consists of 52k IP addresses to block. When I select the list and choose the option to load it in Brave responds with a ‘wait’ or close message on the NAS UI page. If I do wait I will get the message once or twice more until it is loaded in. If I look to do the same operation using Safari on the Mac it completes in less than 3 seconds.
Similarly once the list has been loaded if I ‘okay’ it to apply it I again get similar delays, on Safari it completes within 3 seconds.
I’ve no idea if this is caused by internal caching or another setting. I’d love to be able to solve the issue.
Any assistance is appreciated.

Does it occur on another file, in another folder location?

Does opening a jpg in Brave work?

Everything else seems to work just fine. It seems it’s not only Brave, tests show that the issue is there with Microsoft Edge and Vivaldi. So it may well be a Chromium based browser issue.

Looks like I’ve got some testing to do - removing extensions etc to see if that helps (I don’t think it will though).

Removing all extensions, clearing caches and even rebooting the NAS hasn’t helped at all.

Does opening a different file, from a different location make any difference?

No it makes no difference at all.