Debugging per [1], did not show anything new.
There just is no activity on the actual access of /home all I see is the 
trigger for /home registering at startup.

Startup:
ubuntu@xenial-autofs-client:/$ sudo automount -f -v --debug
Starting automounter version 5.1.1, master map /etc/auto.master
using kernel protocol version 5.02
lookup_nss_read_master: reading master file /etc/auto.master
parse_init: parse(sun): init gathered global options: (null)
lookup_read_master: lookup(file): read entry +dir:/etc/auto.master.d
lookup_nss_read_master: reading master dir /etc/auto.master.d
lookup_read_master: lookup(dir): scandir: /etc/auto.master.d
lookup_read_master: lookup(file): read entry /-
master_do_mount: mounting /-
automount_path_to_fifo: fifo name /var/run/autofs.fifo--
lookup_nss_read_map: reading map file /etc/auto.nfs
parse_init: parse(sun): init gathered global options: 
nosymlink,fstype=nfs,nfsvers=3,rw,hard,intr,rsize=8192,wsize=8192
mounted direct on /home with timeouts disabled
do_mount_autofs_direct: mounted trigger /home
st_ready: st_ready(): state = 0 path /-

It is the open syscall itself that fails:
0.000029 open("/home", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = -1 ELOOP 
(Too many levels of symbolic links) <0.000012>

So we must have set up the kernel/trigger to be broken - no userspace component 
active at the time (although it might have set it up wrong before).
But since I haven't found fixes in autofs maybe it is fixed in the kernel then?

Yes, here I found a fix.
Installing linux-virtual-hwe-16.04 (since I was in a VM to test) resolved the 
issue.
With the same setup I can now mount /home just fine again on Xenial.

On a bare metal system you likely want linux-generic-hwe-16.04 instead.

I'm adding a kernel task to potentially identify and backport the fix to the 
4.4 kernel, but since after so much time it isn't in the stable releases 
chances are that it is hard to backport.
Until then you can get this issue resolved with the -hwe kernels.

[1]:
https://help.ubuntu.com/community/Autofs#Debugging_Auto_Mount_Problems

** Also affects: linux (Ubuntu)
   Importance: Undecided
       Status: New

** Also affects: linux (Ubuntu Xenial)
   Importance: Undecided
       Status: New

** Also affects: autofs5 (Ubuntu Xenial)
   Importance: Undecided
       Status: New

** Also affects: linux (Ubuntu Bionic)
   Importance: Undecided
       Status: New

** Also affects: autofs5 (Ubuntu Bionic)
   Importance: Undecided
       Status: New

** Changed in: autofs5 (Ubuntu Bionic)
       Status: New => Invalid

** Changed in: autofs5 (Ubuntu Xenial)
       Status: New => Invalid

** Changed in: autofs5 (Ubuntu)
       Status: Confirmed => Invalid

** Changed in: linux (Ubuntu)
       Status: New => Fix Released

** Changed in: linux (Ubuntu Xenial)
       Status: New => Confirmed

** Changed in: linux (Ubuntu Bionic)
       Status: New => Fix Released

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https://bugs.launchpad.net/bugs/1827286

Title:
  autofs  - "Too many levels of symbolic links" after apt upgrade

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