MarcM

@Brulti , @gr5 - Thank you for your replies. Perhaps the S5 was not the right machine for me to have purchased. While I appreciate all the 100+ settings that are available in Cura which can control things like fan speed and build plate temp and nozzle temp and print speeds, etc., what I really need is a plug-and-play tool. I suppose the Cura/Ultimaker combo is appropriate for those who have a good understanding of the dynamics of 3D printing and have the time to work through complications and find a solution - - or, as @gr5 has offered, relying on others' expertise and experience to walk through a solution. But this S5 was intended to get up-and-running on some prototypes which work the first time, not to be a 3D printing experiment and education tool to learn the intricacies involved. The glossy marketing materials state that the S5 can print PC--and indeed it can. What it doesn't say is that it won't successfully print PC with the default settings in Cura. If PC needs a particular fan speed and/or plate temperature to build successfully, my thought is that's something Team Ultimaker should incorporate into a release of Cura, not something simply to be left to the Ultimaker Community to figure out. Honestly, I didn't know what I was getting into. Perhaps the aluminum plate would not have made a difference with PC, but my reseller seemed convinced it would. We'll never know. I'm not wanting to rant or whine too much here, sorry if I already have. I threw away the sagging PC parts that were made months ago, so I have nothing to take photos of. If time and my patience permit, I'll print another PC part, and take you up on your offer for assistance. FWIW, it thankfully seems to print ABS just fine.

@davelnewton - I'm not sure which material you printed with. However, we also experienced accuracy issues and, in talking about it with our reseller, found that while Cura/Ultimaker adjusts print speed and nozzle temps for different materials, there is no accounting for thermal rate of expansion--apparently users are left to figure that out on their own. We did some experimentation here and found that, for ABS, applying a scale factor of 1.0017 (X,Y, and Z) in Cura resolved the accuracy issues (mostly).

@SandervG After I set up my new S5 last year, I test-printed in different materials -- e.g., ABS, CPE+, and PC. For the work I do, (prototype molds for thermoforming) I would really prefer to use PC for its higher temperature durability. The S5 was ordered with the optional cover to retain as much heat in the build chamber as possible. Nonetheless, the results of the printed part were poor with PC, as the material sagged and slumped as it built up, resulting in a misshapen mold. I was anticipating the arrival of the aluminum build plate for its thermal properties as a better platform on which to build a PC part. This is why, for me, a second glass plate is unhelpful. Up-time with part changeovers has not been a challenge. I cannot successfully print PC molds on a glass plate, and now the promise of the aluminum plate has vaporized. Quite disappointing.

@Stefania Dinea -- I am wondering if you were able to overcome this problem from back in August (if so, how?). I got a brand new S5 and started printing at the beginning of September, and yesterday encountered this very problem for the first time. I have no idea why. It is updated to the latest firmware (5.1.7.20181023). The representative who sold me the machine suggested switching off the "flow sensor", as others in this thread have suggested, but that is not a permanent solution, just a work-around. When it is printing, the prints look absolutely normal (not as though it is under-extruding). The spool is not bound. I am quite surprised that there has been only one response from Team Ultimaker in this thread. At the moment it is printing again, but I have low hopes of actually printing through the weekend.