Having 3 cubesat deployment missions running simultaneously totalling 26 cubesats to deploy, I decided to see about completing multiple contracts at once, as the game itself prompts you being able to do (if I recall correctly, it's actually in the tutorial for the first cubesat contract itself). I designed a craft with a payload consisting of 20 cubesat deployers and set about completing the two contracts I have for 9 cubesats (C#97 & C#98). I assigned the deployers to the appropriate contract and then assigned the two spares to the remaining contract (C#95) to be sure that they don't automatically get assigned to one of the two that I'm completing in this launch.
Upon proceeding to the launch pad, I get the "wrong craft" notifier next to the contracts - not a problem, I can just click the button to reassign the contract to the current craft. C#98 is all good to go, ticking the "launch with 9 cubesat deployers" requirement and showing that I'm good to go for launch. C#97, however, despite having 9 on-board cubesats assigned, is insistent that I do in fact not have 9 cubesats on board.
I triple-checked my assignment of the contracts in the designer, and I relaunched. I got the same issue. I'm not sure what's going on here but, despite being prompted that it's possible to do so, attempting multiple cubesat missions in a single launch does not work. Even as I type this I feel somehow skeptical that this is the case, and if it turns out that I have in fact overlooked something please do let me know, but as far as I can tell it simply isn't possible to attempt multiple cubesat deployment contracts in a single launch.
Additional note: in constructing the craft, I initially designed it for 12 cubesats (as I'd misremembered how many were required for the contracts), and did so by placing 6 of them along one side in two rows of 3 and then using the quick symmetry tool to replicate them onto the other side (regular symmetry didn't work, presumably on account of being tied to contracts). The bottom 8, however, were individually placed later on. I don't think this affects anything, but I thought I'd mention it in case the symmetry method used could be the culprit.
Note for the game file: There are many craft saved to the designer, but the one relevant to this bug report is "Cubesat IV-20" and the launchpad I'm using is Ali Launchpad.
@AndrewGarrison Good to know, thanks :) As I said in my other reply I recreated the craft, so no need to fix up the xml file, thank you for the offer though