It's hard to say for certain without seeing the code. But if an automated accessibility checker is flagging it, it's probably violating WCAG. Specifically, SC 1.1.1 Non-text Content specifies that decorative images (like your icons) need to be "implemented in a way that it can be ignored by assistive technology."
If you had full control over the code here, the best thing to do would be to hide the icons from assistive technology altogether by either marking them with `alt=""` or `aria-hidden="true"`. Unfortunately, this seems like an Esri-side bug. I would recommend reporting it to them.
It's also worth noting that even though this bug isn't under your control, the ADA Title II expansion rule specifies that jurisdictions are still required to meet WCAG 2.1 AA even if a third party provides the service:
The rule applies to web content that a state or local government provides or makes available. This includes when a state or local government has an arrangement with someone else who provides or makes available web content for them.
The good news is that this is a relatively low-impact WCAG violation. It might be a little annoying and initially confusing for a non-sighted user, but it's not obscuring information and there's a pattern that people will likely catch on to.
P.S. I am not a lawyer!
