The path exists and I can access it as a user.
If it helps, /mnt/mdata
is a mergerfs volume
The strace log is too big (26.8MiB), here is the interesting part:
3152 stat("/mnt/mdata/Dank-PC/181107-0042/Archive/VSC_MP1.ISO", <unfinished ...>
3148 stat("/mnt/mdata/Dank-PC/181107-0042/Archive/VSC_MP1.ISO", <unfinished ...>
3152 <... stat resumed> {st_mode=S_IFREG|0777, st_size=57065472, ...}) = 0
3152 lstat("/mnt/mdata/Dank-PC/181107-0042/Archive/VSC_MP1.ISO", {st_mode=S_IFREG|0777, st_size=57065472, ...}) = 0
3152 stat("/mnt/mdata/Dank-PC/181107-0042/.hashes/Archive/VSC_MP1.ISO", <unfinished ...>
3148 <... stat resumed> {st_mode=S_IFREG|0777, st_size=57065472, ...}) = 0
3148 openat(AT_FDCWD, "/mnt/mdata/Dank-PC/181107-0042/Archive/VSC_MP1.ISO", O_RDONLY|O_NOATIME|O_CLOEXEC) = -1 EPERM (Operation not permitted)
3148 stat("/mnt/mdata/Dank-PC/181107-0042/Archive/", {st_mode=S_IFDIR|0777, st_size=4096, ...}) = 0
3152 <... stat resumed> {st_mode=S_IFREG|0777, st_size=394, ...}) = 0
3152 openat(AT_FDCWD, "/mnt/mdata/Dank-PC/181107-0042/.hashes/Archive/VSC_MP1.ISO", O_RDONLY|O_CLOEXEC <unfinished ...>
3148 poll([{fd=52, events=POLLOUT}], 1, 300000) = 1 ([{fd=52, revents=POLLOUT}])
3148 sendto(52, "\0", 1, MSG_NOSIGNAL, NULL, 0 <unfinished ...>
3152 <... openat resumed> ) = 80
3152 lseek(80, 0, SEEK_SET <unfinished ...>
3148 <... sendto resumed> ) = 1
3152 <... lseek resumed> ) = 0
3148 stat("/etc/localtime", <unfinished ...>
3152 read(80, <unfinished ...>
3148 <... stat resumed> {st_mode=S_IFREG|0644, st_size=2265, ...}) = 0
3141 <... poll resumed> ) = 1 ([{fd=79, revents=POLLIN}])
3153 <... poll resumed> ) = 1 ([{fd=77, revents=POLLIN}])
3152 <... read resumed> "\377\377\377\377\377\377\377\377", 8) = 8
3148 write(1, "2018-11-07 15:46:52: FileSrv: In"..., 55 <unfinished ...>
3141 recvfrom(79, <unfinished ...>
3153 poll([{fd=77, events=POLLIN}], 1, 60000 <unfinished ...>
3152 read(80, <unfinished ...>
3141 <... recvfrom resumed> "4\0\0\0LOG 5-2-Error while download"..., 8192, MSG_NOSIGNAL, NULL, NULL) = 83
3141 futex(0x55adfa6fca78, FUTEX_WAIT_PRIVATE, 2, NULL <unfinished ...>
3153 <... poll resumed> ) = 1 ([{fd=77, revents=POLLIN}])
3152 <... read resumed> "\177\0\0\0AN\360\244", 8) = 8
3148 <... write resumed> ) = 55