Your post indicated that you have firmware 2.1.8, which to my knowledge does not have any logging failure issue reported elsewhere. The HTTP GET command you tried returns the correct log data so I don’t know why it wouldn’t work. One thing you can try is to turn on your browser’s Developer Tools (in Chrome, you can turn on menu Tools -> Developer Tools) and then go to the View Log page. The console in the developer tools tells you what may have gone wrong when retrieving log.
For future reference: I suggest that you submit support questions as support tickets, instead of just posting it on the forum. We don’t check forum regularly so your questions are likely to get delayed here. The reason we ask you to submit support tickets is that we need to look up your order to check which version of controller you have, and in many cases ask you to export and attach your controller’s configurations, which are not suitable for posting on the forum. Thanks.