Could someone with JS knowledge affirm that the swap is fine?
Try a swap like this [rttFloatTexture2, rttFloatTexture] = [rttFloatTexture, rttFloatTexture2];
Also try an indexed array of textures and only swap the integer index to be extra sure that your problem isn't there (that it might copy the texture instance instead of the reference, etc).
But I feel I'm totally off here and the problem is something completely else
Maybe also try binding your vertex buffers, setting the viewport, etc, every time in the loop to rule out that it gets unbound or something...