If the blocks are loose on the handles, then one or both the alignment pins are probably protruding excessively. With a hammer and punch, you can seat them slightly deeper. Usually it's only one that's causing the stickiness.
I loosen off the sprue plate - it is quite loose, not even snug, certainly not held tightly. When I pour, I hold the dipper against it, which holds it flat against the plate - or when the lead it up to temp, pour from above. With a bottom pour pot, the plate wants to sit flat, and does. Lead does not harden above the flat sitting plate.
Sounds as if yours is bent & arches up when the screw is tightened. I cast with a loose screw -
![Grin ;D](https://americanlongrifles.org/forum/Smileys/default/grin.gif)
I use thick, heavily padded gloves - for opening the plate - not a mallet, hammer or stick. Use of any tool on the sprue plate is the reason for bent sprue plates. I use a hammer handle (same one for 30 years now) for tapping the hindge pin to drop out balls that stick slightly. I use Rapine mould prep or MsMoly spray in the blocks to prevent lead sticking and to help the balls drop out. Both work better than candle or lighter soot.