Can the number of neutrons in an isotope make a big difference, there are a few elements which have a wide range of isotopic weights, if a property was quite delicate I’d expect such changes to be quite apparent, tricky for millisecond half lives.
Also I have subscript envy, and shall scour the Internet as to how to do subscripts in HN.
Some small differences might crop up in things that depend explicitly on the mass of the nucleus (e.g. sound propagation, density). But given adding a few neutrons in heavy nucleus is a change of order a percent or so in mass it isn't likely to be dramatic.
AI, and Hg are next to each other on the periodic table, just on the metal / non-metal boundary, beneath them are the Rg, and Cn.
Rg Roentgenium has a short half life, but seems to be tricky to make, it is expected to show some Relativistic properties though:
https://en.m.wikipedia.org/wiki/Roentgenium
Cn Copernicum, according to Wikipedia seems to show RQM effects it acting like a noble gas, albeit one with a half-life of at most 28s: https://en.m.wikipedia.org/wiki/Copernicium
If so why only these too? I’d expect there to be several others with mysterious properties too.