Is there a word/phrase/expression to describe a seemingly easy problem?

"Easier said than done" is a current saying for a seemingly easy problem that is actually quite hard to fix.

If you say that something is easier said than done, you are emphasizing that although it sounds like a good idea in theory, you think it would be difficult to actually do it. Collins

• Avoiding mosquito bites is easier said than done.
• I know I should stop thinking of her, but that's easier said than done.

Perhaps "Fixing the symptoms but not the root cause" is what you are looking for. Or "It's anything but child's play."

Some examples are:

1. 'there's more to this than meets the eye'

2. 'a wolf in sheep’s clothing'

It’s harder than it seems/looks/appears/etc.

For example

Enjoying the Moment: It’s Harder Than It Seems.
- https://psychcentral.com/lib/enjoying-the-moment-its-harder-than-it-seems/