All I can say then is that whoever you are paying to fix things is not doing things properly.
There is no way an upgrade can effect a custom SP theme – the upgrade is totally unaware of it’s existence.
There is no way an upgrade can effect a WP theme – we do not and never would touch that.
The only way custom SP code can be changed by an upgrade is if it is made in one of the SP supplied files – core, theme or plugin. And this is also true of WP, WP themes and WP plugins. And this is why here are structures in place within SP to avoid this happening.
I have no idea what you paid your $50 coder to do. If you tell me what they did and what they changed then I can tell you what was wrong.
Your forum states quite clearly in the about popup that is is using the ‘default’ SP theme. So if your coder changed that then you must expect those changes to be destroyed if you update that theme. We state over and over again that if you make such changes you need to do so in a copy/custom theme to avoid this happening. So whoever made changes – assuming they did – ignored this advice.