Thanks for the logs.
Looks like you’re hitting a TimeMachine SMB Bug when setting the Time Machine Max Size parameter in the admin UI. Please set the Max Size for TM Backups to default. You may need to take a new backup or use AFP to workaround the issue.
[2021/02/25 20:29:25.213791, 0] …/source3/smbd/service.c:885(make_connection_snum)
CIFS: [ipv4:192.168.1.27:54000] connected to [TimeMachineBackup] as user [nobody].
[2021/02/25 20:29:25.233686, 0] …/lib/util/charset/codepoints.c:16656(get_conv_handle)
dos charset ‘CP850’ unavailable - using ASCII
[2021/02/25 20:29:25.300195, 0] …/source3/modules/vfs_fruit.c:6995(fruit_tmsize_do_dirent)
fruit_tmsize_do_dirent: tmsize overflow: bandsize [134217728] nbands [1026]
[2021/02/25 20:29:25.300267, 0] …/source3/smbd/dfree.c:307(sys_disk_free)
sys_disk_free: VFS disk_free failed. Error was : Success
https://linux.debian.bugs.dist.narkive.com/c4i4Xkt0/bug-974868-samba-can-t-serve-size-limited-time-machine-shares-on-i386
https://bugzilla.samba.org/show_bug.cgi?id=13622