There is a cap on the number of notifications (2000). However, date should not matter. Also, I don't know why the oldest notification would go backwards from 2016-01-27 to 2016-01-11. If it's expiring normally, oldest notification should go strictly forward in time.

His user ID is 1206692. He currently has 300, much below the limit, so this needs investigation:

mysql:research@s2-analytics-slave [ruwiki]> SELECT user_id, user_name from user where user_name = '1234qwer1234qwer4';
+---------+-------------------+
| user_id | user_name         |
+---------+-------------------+
| 1206692 | 1234qwer1234qwer4 |

mysql:research@x1-analytics-slave [ruwiki]> SELECT COUNT(*) FROM echo_notification WHERE notification_user = 1206692;
+----------+
| COUNT(*) |
+----------+
|      300 |
+----------+
1 row in set (0.00 sec)

Are all the notifications in question still in the database? I wonder if this might be a problem with the special page's pagination code or the JS for the More button or something.

With Special:Notifications page re-design (incl pagination) - it's difficult to investigate the issue.

I checked db for possible (and obvious) discrepancies - all seems to be in place.

I also have this problem in cswiki. My top number is 99 though I'm sure I became many different notifications since Echo first deployment (it seems similar thing is discussed at T123338 as well).

Update: my top number in cswiki is now 149. Moreover, I can no longer see arrows on Special:Notifications on Wikidata (there are only 50 last notifications).

I can't reproduce this, so perhaps this has been fixed?

In T129638#5883779, @TerraCodes wrote:

I can't reproduce this, so perhaps this has been fixed?

Seems so, but I don't see the first "welcome" notification.