ENVIRONMENT and STATS
For syncing clients:
From chrome://version, please provide the OS and Chrome build number.

Google Chrome	59.0.3071.36 (Official Build) beta (64-bit)
Revision	0a97305f0587704e901b20cc4060c997d6c4eaff-refs/branch-heads/3071@{#365}
OS	Linux

From about:sync, copy/paste the tab contents here, or select the Data tab
and click [Dump sync events to text].

Summary
Summary	Sync service initialized
Version Info
Client Version	Google Chrome Linux 59.0.3071.36 (0a97305f0587704e901b20cc4060c997d6c4eaff-refs/branch-heads/3071@{#365}) beta
Server URL	https://clients4.google.com/chrome-sync
Identity
Sync Client ID	Ctx8HfB2Cr6PKB02YfLKqw==
Invalidator Client ID	ITyiO1RmzUGh4CUKRDKWGw==
Username	coliny@google.com
Credentials
Requested Token	Tuesday, May 9, 2017 at 10:32:41 AM
Received Token	Tuesday, May 9, 2017 at 10:32:41 AM
Token Request Status	OK
Next Token Request	not scheduled
Local State
Server Connection	OK since Tuesday, May 9, 2017 at 10:32:42 AM
Last Synced	Just now
Sync First-Time Setup Complete	true
Sync Backend Initialization	Started
Syncing	false
Local sync backend enabled	false
Local backend path	Uninitialized
Network
Throttled	false
Retry time (maybe stale)	Scheduler is not in backoff or throttled
Notifications Enabled	true
Encryption
Explicit Passphrase	false
Passphrase Required	false
Cryptographer Ready	true
Cryptographer Has Pending Keys	false
Encrypted Types	Passwords, WiFi Credentials
Has Keystore Key	true
Keystore Migration Time	Thursday, April 9, 2015 at 10:30:20 PM
Passphrase Type	PassphraseType::KEYSTORE_PASSPHRASE
Passphrase Time	No Passphrase Time
Status from Last Completed Session
Sync Source	LOCAL
GetKey Step Result	UNSET
Download Step Result	UNSET
Commit Step Result	SYNCER_OK
Running Totals
Notifications Received	62
Updates Downloaded	1552
Tombstone Updates	380
Reflected Updates	1434
Successful Commits	2645
Conflicts Resolved: Client Wins	0
Conflicts Resolved: Server Wins	0
Transient Counters (this cycle)
Encryption Conflicts	0
Hierarchy Conflicts	0
Server Conflicts	0
Committed Items	1
Transient Counters (last cycle of last completed session)
Updates Downloaded	0
Committed Count	1
Entries	9934
Nudge Source Counters
Server Invalidations	0
Local Changes	0
Local Refreshes	0
Sync Protocol Log
5/9/2017, 12:23:16 PM Commit Request
Item count: 1
Contributing types: Favicon Tracking
5/9/2017, 12:23:16 PM Commit Response
Result: SYNCER_OK
Type Info
Model Type	Group Type	Total Entries	Live Entries
Bookmarks	Active: GROUP_UI	312	312
Preferences	Active: GROUP_UI	73	73
Passwords	Active: GROUP_PASSWORD	196	196
Autofill Profiles	Active: GROUP_DB	5	5
Autofill	Active: GROUP_DB	1	1
Autofill Wallet	Active: GROUP_DB	3	3
Autofill Wallet Metadata	Active: GROUP_DB	4	4
Themes	Active: GROUP_UI	2	2
Typed URLs	Active: GROUP_HISTORY	8201	8201
Extensions	Active: GROUP_UI	32	32
Search Engines	Active: GROUP_UI	156	156
Sessions	Throttled	474	474
Apps	Active: GROUP_UI	21	21
App settings	Active: GROUP_FILE	12	12
Extension settings	Active: GROUP_FILE	5	5
History Delete Directives	Active: GROUP_UI	1	1
Dictionary	Active: GROUP_UI	1	1
Favicon Images	Active: GROUP_UI	200	200
Favicon Tracking	Active: GROUP_UI	201	201
Device Info	Active: GROUP_NON_BLOCKING	13	13
Priority Preferences	Active: GROUP_UI	15	15
Managed User Settings	Datatype not ready at config time.	null	null
Managed Users	Active: GROUP_UI	1	1
Managed User Shared Settings	Active: GROUP_UI	1	1
Managed User Whitelists	Datatype not ready at config time.	null	null
Tabs	Passive	null	null

REPRO STEPS
Open tabs on different devices.  Visit chrome://history/syncedTabs.

ACTUAL RESULTS
Synced tabs are not updated; that page says "6 days ago" for other devices.

EXPECTED RESULTS
Synced tabs are updated.

ADDITIONAL INFO
Syncing seems to be working otherwise; for example, deleting a bookmark on one device caused it to disappear on other devices shortly thereafter.

I'm seeing the same behaviour (synced tabs not updated) on my other devices too:  on Chrome OS beta (58.0.3029.89) and on Android Chrome Dev (60.0.3087.3).