Umm. The 3 or 4 hours agitation is probably the problem. Salt sets colours, but the longer the fabric is left in the water, the more the salt-dye reaction changes. Generally, an hour is enough to set deep colour. Longer than that can make it go backwards and fade out.

Re: the hot water– unless it was hot enough to burn, I don't think it would've been too much of a problem. Pasting fibre-reactives is more important than the temp of the initial mix water.