Australia

Imo you were too vague in your conditions.

https://doi.org/10.1001/jamapediatrics.2024.5542

This systemic review and meta-analysis includes this (weak!!) negative health result even at <=1.5mg/L fluoride/water (1.5mg/L being the upper limit for drinking water that the WHO recommends according to many papers including this paper, but which annoyingly doesn't seem to have an up-to-date page on the WHO website to confirm with).

Sixty-four studies reported inverse associations between fluoride exposure measures and children’s IQ. Analysis of 59 studies with group-level measures of fluoride in drinking water, dental fluorosis, or other measures of fluoride exposure (47 high risk of bias, 12 low risk of bias; n = 20 932 children) showed an inverse association between fluoride exposure and IQ (pooled SMD, −0.45; 95% CI, −0.57 to −0.33; P < .001). In 31 studies reporting fluoride measured in drinking water, a dose-response association was found between exposed and reference groups (SMD, −0.15; 95% CI, −0.20 to −0.11; P < .001), and associations remained inverse when exposed groups were restricted to less than 4 mg/L and less than 2 mg/L; however, the association was null at less than 1.5 mg/L. In analyses restricted to low risk-of-bias studies, the association remained inverse when exposure was restricted to less than 4 mg/L, less than 2 mg/L, and less than 1.5 mg/L fluoride in drinking water. (emphasis added)

I would personally consider this to qualify, though I will understand if you want to be more strict. I'm also not the person you were replying to lol.

edit: This one is a bit less ambiguous, though it's not open access https://doi.org/10.1016/j.matpr.2023.05.645 (the language they use also makes it sound like they have an agenda, but I know nothing about the authors)

Fluoride improves tooth structure, preventing inflammation and deterioration. Water fluoridation should not exceed 1.0 mg/L to protect dental plaque and public hygiene [35], [36]. Fluorosis affects teeth once 1.0 mg/L is surpassed. This condition causes tooth stains and cavities.

Which I think qualifies as "suggests it is suspected to be unsafe at recommended levels" if you allow the recommend level to be "some nebulous amount up to 1.5mg/L" and for "unsafe" to be "causes or is associated with negative health effects".