I had never used the anti-erased, so I did some tests, and WOWWW, that's not what I expected! 
Using the eraser tool in anti mode, remove smooth edge like gradient to transparency with anti-aliasing it become harsh edges like no more anti-aliasing...
Going over the alpha with anti erase checked, just become a plain black brush on the alpha channel
Locking the alpha channel in the layer docker, just forbidden the use of the eraser or anti-eraser on the alpha or not...
If I remove the alpha channel on a layer, I can erase (although the BG will appear which is normal) but I cannot anti-erase!?!?!!!
I would recommend to use mask instead...
May be do an "Alpha to selection" (right click on the layer) before using the anti eraser to "protect alpha" but I don't know how you work, and this will prevent to get back what you already erased if it's transparent... So there is no real purpose to do it
IMHO the anti thing should not behave like that, at least not paint black on alpha (which is a kind of logic, but it should not do it, in all case I don't know the math behind the anti-erase so I should not make suppositions)
You might want to report that behavior to https://www.gimp.org/bugs/ (read that page first) then go there > https://gitlab.gnome.org/GNOME/gimp/-/issues/new ,
Before the report, make screenshot of before and after, explain with separated paragraph to be easily readable, over all prepare your bug report before on your preferred office with how to reproduce the different bugs, be clear in your explanations
You can add a link to this thread in your bug report
Using the eraser tool in anti mode, remove smooth edge like gradient to transparency with anti-aliasing it become harsh edges like no more anti-aliasing...
Going over the alpha with anti erase checked, just become a plain black brush on the alpha channel
Locking the alpha channel in the layer docker, just forbidden the use of the eraser or anti-eraser on the alpha or not...
If I remove the alpha channel on a layer, I can erase (although the BG will appear which is normal) but I cannot anti-erase!?!?!!!
I would recommend to use mask instead...
May be do an "Alpha to selection" (right click on the layer) before using the anti eraser to "protect alpha" but I don't know how you work, and this will prevent to get back what you already erased if it's transparent... So there is no real purpose to do it
IMHO the anti thing should not behave like that, at least not paint black on alpha (which is a kind of logic, but it should not do it, in all case I don't know the math behind the anti-erase so I should not make suppositions)
You might want to report that behavior to https://www.gimp.org/bugs/ (read that page first) then go there > https://gitlab.gnome.org/GNOME/gimp/-/issues/new ,
Before the report, make screenshot of before and after, explain with separated paragraph to be easily readable, over all prepare your bug report before on your preferred office with how to reproduce the different bugs, be clear in your explanations
You can add a link to this thread in your bug report