Maybe the software needs to solve [re-link] the relationships one by one otherwise how it would handle relationships of other to be dissolved activities at the same time as you are asking.

Be careful with "dissolve" it can easily distort the schedule as to make it invalid because it makes some simple assumptions that might not be true. For example:

Activity 1, d=5 days

Activity 2, d=5 days predecessor links; 1 to 2 SS 5 days lag, 1 to 2 FF 5 days lag

Activity 3, d=5 days predecessor links; 2 to 3 SS 10 days lag, 2 to 3 FF 10 days lag

If you dissolve Activity 2 what will be the new relationships and which lag value, why not the other value? If Activity 2 had links to other activities this can get further complicated.

What if lag calendars are different, then which prevails?

Good practice calls for attention to these details, updating or re-scheduling is to be done right, no matter if it takes longer, Hammer's Rule [make it fit with a hammer] is no good here.

Maybe Dissolve functionality should be expanded as to display a dialog box after each dissolve, a window that will tell you what was before, how it was changed [including all relevant information such as lag values, lag calendars ...] an the option to cancel the dissolve, until then just avoid it unless you are sure it will perform 100% as you expect it.