You’re conflating the conscious mind’s thoughts and experiences with consciousness itself.
Thoughts are the product of the mind, we may agree, correct? And we may have several distinct thoughts, yes? Now, if a given cause of an effect is constant in all qualities then there can only be two explanations for the difference in effect derived from such mind. Either the surrounding conditions changed or the the effects are random. If its the first, then we cannot be referring to a mind, for one, because a mind is said to have the power of agency over what occurs in the realm of mental phenomena, but if all thoughts are different because of surrounding conditions and not because of any difference in position by the mind then there cannot be any agency in said mind, which contradicts the idea of mind. Further, to say that the change in effect is due to a difference in surrounding conditions rather than the cause, the solipsist would be making an admittance to the idea of surrounding condition in their defense of the individuals mind being noncontingent, which would, of course, contradict their initial position. As such, this compromise cannot be made by the solopsist.
If the effect is different due to a random nature, then it too reaches the same conclusion as the first alternative, that being the agency of the mind is robbed.
Given this, we must say that the mind can change in order to explain the difference in thoughts as well as preserve the agency of the given entity.