rows.Next() halts after some number of rows - oracle

Question

Im newbie in Golang, so it may be simple for professionals but I got stuck with no idea what to do next.
I'm making some migration app that extract some data from oracle DB and after some conversion insert it to Postges one-by-one.
The result of native Query in DB console returns about 400k of rows and takes about 13 sec to end.
The data from Oracle extracts with rows.Next() with some strange behavior:
First 25 rows extracted fast enough, then about few sec paused, then new 25 rows until it pauses "forever".
Here is the function:
func GetHrTicketsFromOra() (*sql.Rows, error) {
rows, err := oraDB.Query("select id,STATE_ID,REMEDY_ID,HEADER,CREATE_DATE,TEXT,SOLUTION,SOLUTION_USER_LOGIN,LAST_SOLUTION_DATE from TICKET where SOLUTION_GROUP_ID = 5549")
if err != nil {
println("Error while getting rows from Ora")
return nil, err
}
log.Println("Finished legacy tickets export")
return rows, err
}
And here I export data:
func ConvertRows(rows *sql.Rows, c chan util.ArchTicket, m chan int) error {
log.Println("Conversion start")
defer func(rows *sql.Rows) {
err := rows.Close()
if err != nil {
log.Println("ORA connection closed", err)
return
}
}(rows)
for rows.Next() {
log.Println("Reading the ticket")
ot := util.OraTicket{}
at := util.ArchTicket{}
err := rows.Scan(&ot.ID, &ot.StateId, &ot.RemedyId, &ot.Header, &ot.CreateDate, &ot.Text, &ot.Solution, &ot.SolutionUserLogin, &ot.LastSolutionDate)
if err != nil {
log.Println("Error while reading row", err)
return err
}
at = convertLegTOArch(ot)
c <- at
}
if err := rows.Err(); err != nil {
log.Println("Error while reading row", err)
return err
}
m <- 1
return nil
}
UPD. I use "github.com/sijms/go-ora/v2" driver
UPD2. Seems like the root cause of the problem is in TEXT and SOLUTION fields of the result rows. They are varchar and can be big enough. Deleting them from the direct query changes the time of execution from 13sec to 258ms. But I still have no idea what to do with that.
UPD3.
Minimal reproducible example
package main
import (
"database/sql"
_ "github.com/sijms/go-ora/v2"
"log"
)
var oraDB *sql.DB
var con = "oracle://login:password#ora_db:1521/database"
func InitOraDB(dataSourceName string) error {
var err error
oraDB, err = sql.Open("oracle", dataSourceName)
if err != nil {
return err
}
return oraDB.Ping()
}
func GetHrTicketsFromOra() {
var ot string
rows, err := oraDB.Query("select TEXT from TICKET where SOLUTION_GROUP_ID = 5549")
if err != nil {
println("Error while getting rows from Ora")
}
for rows.Next() {
log.Println("Reading the ticket")
err := rows.Scan(&ot)
if err != nil {
log.Println("Reading failed", err)
}
log.Println("Read:")
}
log.Println("Finished legacy tickets export")
}
func main() {
err := InitOraDB(con)
if err != nil {
log.Println("Error connection Ora")
}
GetHrTicketsFromOra()
}