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Could be worth shoving some glitter or other coagulant in there, or using a slightly thicker sealant like Orange Seal.
If the cut's too big it can't really clog properly, I rode over something sharp on my commutomtb the other day and it just spurted everywhere, but it was a good 1/2cm slice. Just about sealed at 10psi, but wouldn't hold when I pumped it up.
Gonna buy some dynaplugs/other tyre anchovies I think.
The fizz and bubble bit was happening.
It would seem to be good, I'd start riding again and then in a few minutes, the sound of air escaping would resume.