The error happens here:

Jan 24 17:10:06 controller mount.davfs: FUSE_READDIR:
Jan 24 17:10:06 controller mount.davfs:   n 0x10033e1cc00, fd 6
Jan 24 17:10:06 controller mount.davfs:   pid 10114
Jan 24 17:10:06 controller mount.davfs:   size 65536, off 0
Jan 24 17:10:06 controller mount.davfs: RET: Invalid argument

The fuse kernel module tries to read a block of 65536 Bytes. But the buffer for davfs2-kernel-communication is only 16 KiB and davfs2 returns an error.

I don't know why fuse does this on ppc64le and it is hard for me to debug because I don't have any ppc hardware.

What you could try first:
Set option "buf_size 65" (or something bigger than 65, e.g. 128) in your davfs2.conf file. Now the buffer should be big enough, except when the kernel now requests more than 64 KiB of data.

The error might be caused by different integer format of ppc64. If davfs2 defines the wrong data type somewhere in the communication with the kernel this might result in the kernel getting wrong information about maximum read size. Maybe someone (you?) with this kind of hardware could try to look at the bits?

Werner