Hi. Sorry to hear about your problem. Can you enable debug = 2 in config.php and then attach the complete error message, please?

An easy fix would be to add the "hash" column to the notifications table:

ALTER TABLE <prefix>_notifications ADD COLUMN hash VARCHAR(64) DEFAULT NULL;

ALTER TABLE <prefix>_notifications ADD COLUMN hash VARCHAR(64) DEFAULT NULL;

result

16:01:07 ALTER TABLE notifications ADD COLUMN hash VARCHAR(64) DEFAULT NULL Error Code: 1060. Duplicate column name 'hash' 0.012 sec

select * from notifications:
1 user 1 Database update The database has been updated from version 258 to version 260. read 1 default 2016-09-01 14:04:35 2016-09-01 14:05:01
2 user 2 Database update The database has been updated from version 258 to version 260. new 1 default 2016-09-01 14:04:35
3 user 1 Database update The database has been updated from version 260 to version 263. new 1 default 2017-09-28 14:33:31
4 user 2 Database update The database has been updated from version 260 to version 263. new 1 default 2017-09-28 14:33:31

It looks, that Limesurvey has started to work. Is it possible, that browser has not cleared cache properly?

No, LimeSurvey still had the old database scheme cached. Most of the time this resolves itself after a few minutes but it would be nice if it did not happen in the first place.