Is it normal for a developer to go the customers to troubleshoot a certain problem?

I mean, we got technicians & support department

Depends on the company but normally not.

If you sell software on premise some calls are unavoidable.

@Lensflare should be right in the whole world, but depending on where the company is, developers are considered "computer kids" and all "computer stuff" falls on them.
Including machinery like the A/C and microwave oven.
When I was a wee lad, I was asked to travel 300Km to install an app in the client's systems. Our company's app was a *website*. They were asking me to install a website. Because it was their company's policy to have their vendors install every system purchased.
Never underestimate the amateurism of company managers, especially regarding departments they are proud to know nothing about.

idk

actually I was sort of annoyed I was barred from talking to customers

on other instances I really grew to appreciate the q&a guy for having to deal with the client's test team all the time. he was bothered all the time and he respected my time so it was a nice bottling role that improved my quality of life

however... project managers... in that case there are many instances where they're just plain stupid and stubborn about it. I got one once who just dictated the whole team and told us to do nonsense the client never asked for. I would have preferred to talk to the customer instead of have her, because she created problems. worse, she'd have meetings that lasted hours where she would just vent about the client ???

so I think it's not the worst. I'd assume dealing with customers you get some of the good, some of the bad. harder to fire a bad project manager I think if you get unlucky enough to have one like that