When logrt[] analyzes a log file which ends with a large record (over 256 kB) without newline at the end then the record is reported to server (if it matches the regexp).
If there is a newer log file then logrt[] proceeds with analyzing it and skips the first record (this is incorrect).

Steps to reproduce:
1) Create the older log file with a large record without newline at the end, e,g.

$ perl -le 'print "a"x300000' | dd bs=1 count=299999 > test.log299999

2) Create the newer log file, e,g.

$ echo test1 > test.log
$ echo test2 >> test.log

Now there are 2 test files, with timestamps, e.g.

$ ls -ltr test*                                                         
-rw-r--r-- 1 zabbix zabbix 299999 jul  8 17:55 test.log299999
-rw-r--r-- 1 zabbix zabbix     12 jul  8 17:56 test.log

Create a new test item like

        logrt[/home/zabbix/^test.log]

Observe in "Monitoring->Latest data" that record "test1" is missing:

2021-07-08 17:58:47 1625756327 "test2"
2021-07-08 17:58:47 1625756327 aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
.....

The record should be:
  - large,
  - the last record in the file,
  - without newline at the end
for this error to happen.