I think I figured it out. I don't have any streamlines here to compare it with, but I believe the "chambering but not firing" jam may be a combination of the following factors:
A: ZS Elites and Elites have a larger inner diameter and denser foam than Streamlines, making them hug the dart post tighter in the Longshot's breach. (If my memory serves correctly.)
B: The Longshot does not have anywhere near a 100% seal in it's breach. The amount of force may actually not be enough to make the ZS Elites move from the dart post.
This is mostly speculation, I have a feeling covering the air-release hole in the blaster may help alleviate this issue. It makes sense that the blaster would need a "breaking in" period, so that the grease spreads out more evenly and improves the seal enough to make the blaster fire elites to some degree of effectiveness.
Like Naturalman said, pretty much the same as the 2006 Longshot, with a very hasty hotfix to increase compatibility with newer darts.
Since i have a ZSLS and a standard LS, so far, everything is exactly the same, I do not know how elites didn't chamber in certain LS's but everything is the same. Here is my list (in no order) of my pros and cons so far about the ZSLS
*I believe the range is a bit better, but i can't confirm actual lengths. (I was comparing it to my blue LS, the spring is a bit old so that may be a factor)
*A tacticool scope thats orange for all our tacticool needs.
*Its an LS so all the fun stuff can be added on.
*Cost is the first to come to mind, an LS cost 35$ before for the extra front gun and bipod, if they are going to rerelease it for the same price, they should at least included the bipod, (I hated holding up the LS at the bipod rest area? I don't know exactly what to call that)
*The paint, oh my god why turquoise, not everyone is good at painting, (I liked having a spectre barrel because why not) so no attachments can really be added on besides the scope given that match the coloring scheme.
*They didn't make the shell ambidextrous, I use both arms to shoulder blasters I use. They could have easily added a Stryfe style magazine release, everybody likes those. I guess its laziness.
Overall, this ZSLS disappoints me but at least we have more LS's, I hope they make a modernized variant for elite or ZED squad with a pre done shotgun grip, stryfe style mag release, and other various shell changes, thats probably not going to happen but Nerf or Target could've just retailed the ZSLS for a bit cheaper, I think a more appropriate price point would've been 20-30$ but seeing how everything is going up in price, well meh. If you have any requests or questions about the ZSLS feel free to ask, I do not have the scope in my possession anymore but I still have the blaster.