I wanted to chime in here and say that I have also been sorely disappointed with my purchase of the DL4 MKII. I own two of the original first-generation DL4 pedals, in both of which I've replaced the switches, and in one of which I've also replaced the pots for the knobs. I have used these for nearly twenty years now, and I've always been impressed by their versatility and hardiness, even though the hardware has its weak points. Like many, I see the DL4 as the world's best looping pedal. It's a cool delay, but the looper is where it's at. Even though it has a short recording time, this was more than overcome by the facts that Line6 absolutely nailed the interface, that the audio quality is top-notch (I have heard people say different, perhaps later generations of the DL4 are not as good), and above all, that the software is bulletproof. I can spam the start/overdub button as fast as I possibly can, and the DL4 doesn't mind at all — it just records, stops recording, starts again… as quickly as I can press the button. Same goes with the reverse and half-speed functions. I can let the pedal record, switch to reverse in the middle of a recording, switch to half speed, close the loop with overdub, stop overdub, start again, etc. all as rapidly as my foot can possibly perform, and the DL4 keeps up. It's a wonderful pedal.
On the other hand, the software on the MKII seems to have been developed with a much less comprehensive approach. Glitches abound, and not just with crazy button spamming. Laying down a long-ish loop today, closing it out, switching to half-speed and reverse, and recording again, yielded a blast of white noise in the middle of the loop, not even coincident with my second punch-in and punch-out… it was just random white noise.
What this most likely indicates is poor code QC, and insufficient testing before coming to market. It may be that the MKII's software is written in a style where conditional flows collide and variables or states get mangled in the shuffle. It could be a fault in the way audio bitrates are handled. It could be poor integration between software and hardware. I really don't know, and tbh it doesn't matter. What matters is, the pedal is unserviceable in its current state. Yes, it's awesome to have a DL4 with super long recording times (for the record, I am using an SD card). But to be frank, the main thing that made the DL4 special was its combination of simple interface and creative flexibility brought on by the robustness of its feature set, and how, if you had a question "well can it do this?" the answer was always "yes."
I wanted a super long recording DL4, but what I have is a glitchy, unreliable piece of gear that no one in their right mind would take on stage in an experimental music rig. So, for people like me it's like it didn't come out.
I hope the engineers at Line6 are working on a follow up to the firmware update they released last year. I hope they're going back to the drawing board with it, and putting whatever they come up with through a comprehensive QC process, testing before they release an update, fixing this stuff. I hope so because I like what they've done in a lot of ways. It's great hardware (albeit with some unfortunate choices regarding indicator lights management), great sounding delays, solid construction, awesome input options.
But unfortunately, because the endurance of the legacy of the DL4 is all about the looper (sorry, that's the truth), the MKII is not usable in its current state.