Compare with the steps I wrote down here: DietPi as WiFi router? - #33 by MichaIng
In your case, try
ifup --force wlan1
systemctl restart hostapd
Compare with the steps I wrote down here: DietPi as WiFi router? - #33 by MichaIng
In your case, try
ifup --force wlan1
systemctl restart hostapd