Ok so this is what i've found so far.
I first tried deleting all the temp files listed as safe to delete, and then doing a game repair. Nothing changed with my saved games so I moved on to creating a new household of one and used only some of the in game cheats for money and mood to get her up to lvl 5 gardening quickly.
Any cuttings she takes from the home lot are correct. They are named as to what plant they come from and everything. Any cuttings taken from other plants in the same neighborhood still have the same problem I have been experiencing. They are missing the plant name but otherwise look identical to cuttings from the home lot.
When splicing these shoots, they start out acting correctly, they start the grafting animation and they work for the Freelance Botanist Aspiration in that they give credit for grafting, however the animation look like it fails at this point and resets and nothing appears to happen to the plant. The shoot that looks normal performs normally, gives credit, and looks like a completed animation, also the plant goes back to an earlier growth stage and says it's a combo plant now.
Only other thing I can think of to say is I am playing the game on Win 10 64bit. I have Sims Digital Deluxe version. with Get Together, Spa Day, Outdoor Retreat, Spooky Stuff, Cool Kitchen Stuff, Perfect Patio Stuff, Luxury Party Stuff, last years free Holiday Celebration Pack, Along with the digital deluxe addons that came with that. However this same problem was happening before I got Outdoor Retreat, Spooky Stuff and Cool Kitchen Stuff all at the same time just before the last update.
I will upload my save game file to that link you provided Crin with my name from here.
hope this helps squash this. :D
Also if you or the EaGuru think of something else for me to try with this clean game I have now let me know.