Yeah, when I first looked into this, I found all these popular sites talking about tinnitus and infection, but couldn't track down any sources. Wikipedia just cites those websites. One actually does give a source: Journal of Hearing Sciences, 2006: 9-10. This seems to be made up by its "SEO professional" author. ("Journal of Hearing Science" at least exists, but started in 2011. Bizarre.)

I don't remember finding anything especially scientific and reliable on risks when I first looked into it. The best I could do was Ear Infection and the Use of Hearing Protection (1985), a review of epidemiological studies by a researcher employed by an earplug manufacturer, mostly concerning workplace use.

Anecdotal comments abound, but controlled studies are "conspicuous by their absence." By implication the problem is neither significant nor widespread; otherwise it would have drawn greater attention and research interest.

...

Although hearing protection devices should not be worn in the presence of some preexisting ear canal pathologies, and care must be exercised regarding selection and use under certain environmental conditions, regular wearing of HPDs does not normally increase the likelihood of contracting otitis externa.

I don't know how much you want to rely on that. I just follow the manufacturer's instructions for cleaning and reuse, and plan to stop if I notice irritation.