Copie to nextcloud conection refuse

Hi everyone,
i have a raspberry pi 4 with an actual nextcloupi image install. i run it in dns loopback mode, so i can reach the nextcloud from my home and mobile from everywhere. this goes well and i am happywith it. Contacts and Calender works very good.

Now, if i @ home an want to copy my files to my nextcloudpi, i tryon my ubuntu over davs and the copy stops with a tls certifikate error.

over samba copy starts but breaks sometimes.

my raspberry is over wifi with my rooter conected.

i don’t know what i can do to prevent it. i search online for errors like mine - i don’t find something. i search over ssh in my logs, but i don’t know what i shall search… i am not a proffessional.

hope someone has the same error see or has a idea to handle ths issue.

best regards