At work we had three employees at one time that had freshly upgraded to S9s, from S3/S4s. All three ultimately did the 'moisture warning' issue and wouldn't charge unless you used wireless.
I still blame USB-C. I have had a hostile relationship with it ever since it became 'mandated' without my approval. Literally NOBODY asked for this.
The 'moisture detected' error was pretty well-known at the time the S9 was the latest thing. search for 'Galaxy S9 design flaw moisture detected' and you'll get tons of results. It's a well known issue. None of the the mentioned phones EVER got wet.
My main gripe with Type C is that it usually always says it's charging but it drains while it says so. I can't trust it. Never had issues with Micro USB at all. EVER. Always worked if it showed it were charging. Even if you got the 'Battery with X or ! inside it' error it would still charge, just slower than normal. I wouldn't wake up to 18% 'charging' like today.
Micro USB also never had Android Auto issues with my Galaxy S5 either. Now, I'm lucky if I don't have to unplug/replug the damn Z Flip 4 five times before it works. The rest are either my Pioneer deck being blank, or it showing 'no signal/icon with ! inside it' and no connectivity (while the outer display shows plenty of signal) or it not responding to touch/voice control.
As harsh as it sounds, I feel whomever decided that USB Type C was a good idea needs to be lined up and shot. Change for change's sake. Micro USB was never an issue if you aren't an idiot. The little USB symbol faces up, for those who don't know. Even when Apple (and Samsung) had that wonky 30-pin connector, there was a visible icon that showed the 'up' side. But hardly anyone read the frelling manual to know that and blamed the wrong person for being an idiot.
Back in 2014 when Type C first launched (on the Nexus 6) the whole selling point was 'it's reversible!' and that was one of the 'remarks' that CrApple fans used to brag about their lightning connector, 'but you can plug it in either way!' So I always figured that was why USB-C happened in the first place. I wish everyone would stop looking to Apple for advice, or who to follow. I wish Android just remained its own thing like it was in Android 2.3, Gingerbread.