Hi all,
    I'm encountering this issue in a Windows 10/Pg11.5

I followed the thread @ https://postgrespro.com/list/thread-id/2380690

but examining heap pages is far beyond my knowledge, so if any of the gurus would spend some time on it, I would be very grateful.

So, here comes the facts

database0=# select datminmxid from pg_database where datname = current_database();
datminmxid
------------
        365
(1 row)

The CTID of the tuple BEFORE the failing one is 3159,51:

database0=# select ctid from tablename offset 368 limit 1;
ERROR: MultiXactId 12800 has not been created yet -- apparent wraparound
database0=# select ctid from tablename offset 367 limit 1;
   ctid
-----------
(3159,51)
(1 row)

Now, I started issuing the queries

select * from heap_page_items(get_raw_page('tablename',3159));
select * from heap_page_items(get_raw_page('tablename',3160));

and so on for about 5 or 6 pages.
What do I need to search for? 
Or is it better to \copy them to and send 'em as an attachment?
How many pages do I need to search for? 
Until I see the error again?

Thanks in advance
Moreno.-