Why is the first character in the strings replaced by 1 when answering from the database?

Question

PHP

There was a strange problem, an array of data comes from the database, and in all lines the first character is replaced by 1:

Although the data is correct in the database itself:

I noticed that when PHP is downgraded to 5.3, the problem disappears, but this does not suit me, at least because the host version on the entire server, and the rest of the sites fall off. Where to dig? I tried to play around with the mbstring settings and server encodings - but it didn't help.
Drupal 7.59, >=PHP5.4
UPD:
Unfortunately, the request cannot be pulled out, because the data has time to be cached and the data is pulled from the cache tables in which the serialized data. But even there I checked - there are no units of these.
The request itself:

SELECT cid, data, created, expire, serialized FROM dr_cache_field WHERE cid IN (:cids_0)

Answer 1

It is unlikely that the matter is in the request itself, although it is possible in it, so post it here.
It is very similar to the situation when someone added something in the depths of the Drupal code during development (to test something), and then simply forgot to remove it.