It seems that wherever I put my the starting points in Forge, I always spawn in the places where the default objects were deleted. For example, if I use the stacked Sky Bubble canvas and delete the default objects when I finish my map, I keep spawning in mid-air where they used to be. Hence, the first spawn in every new round involves the player dying instantly, which is not particularly desirable. Yes, I've deleted every single starting and respawn point for every gametype and replaced them in all the places that I want, but this glitch still seems to happen. I've found that I've downloaded some of other peoples' maps and the same problem happens - on the first spawn, everyone falls to their death at the old default spawn points. Is this a flaw of Sandbox, a glitch on my copy of the Mythic Map Pack or an easily solved problem?
In Forge you will not always spawn on the starting point of that gametype. I think it sometimes uses the CTF and Slayer starting points. Does it do it in Customs? If it does then thats rather odd.
I have had this problem, and i solved it by going through every gametype and deleting/moving the spawn areas and start points. These can affect you even if you are not in the same gametype.