GRLevelX I have found has always had a problem with data gaps, often with images coming late on days where traffic is high. During outbreaks, every once in a while I'll start getting images in about 10-15 minutes late, with it sometimes dropping out entirely and eventually catching back up. Granted, I use GR2Analyst instead, but I digress.
I never had any major issues with the free NWS data feed until this year. On May 2nd, the radars barely updated at all, maybe one scan every 15 minutes no matter which radar site I went to (and that didn't even turn out to be that big a day). On past big days like Dodge City day 2016, no problems (at least not major, maybe a few minute lag but still got all the scans). I didn't even have issues on April 27, 2011, until some of the actual radar sites started going out due to infrastructure damage.
I have been using GRLevel for 7-8 years or so. I don't ever remember having ongoing problems until this Spring. Mike (in post #4 above) says it is an NWS feed problem. I heard that explanation from someone else this past Spring also. According to Mike, they are working on the problem which is good news.