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I don't know what's hanging up in your case. My advice is to make sure the metal press clamp is well seated over the screw bosses and the screws are fully retracted. There are detents in the metal that keep the clamp in place, but it can easily slide off, especially if it's tilted some. Hold the boom and slider level and top-up. The curved and straight sliders should be identical in that area, so I don't expect any issues.
This may need an entire new post, but I’m interested in the different methods people use for tubeless tires (always trying to learn). For example, the only time I will use a high pressure for a tire is when seating it, and that is without sealant and I don’t recall ever going over the recommended max pressure. Once seated I only press up to the max advertised on the tire, although recommended pressure for weight and tire is usually much less. For sealant, I always add via the valve stem - in other words, I never fill the tire first and then seat the tire to the rim.
Do you just keep adding or you actually clean it out once a year?
I clean it out occasionally. Use a syringe to get the liquid sealant out (and reuse) and then peel the dried sealant out of the tire.
Don’t force it. Most likely is cross-threading, you need to ensure the bb is aligned correctly. Try turning the bb backwards and when you feel a click screw it in. Much less likely is some burr or other defect on the threads.
May as well have them screw the bb in to the correct torque while you’re at it.
Does your BB have thread locker on it? If so, I’d be interested to hear what your LBS has to say about using grease. The Park Tool video on BB installation notes that grease should not be used if thread locker is applied.
