Eu mudei a versão do tds em /etc/freetds/freetds.conf do 8.0 (funcionou antes do upgrade do php 7.1) para o 7.0 em um servidor MSSQL típico. Agora funciona.
Configuração completa
/etc/odbcinst.ini
[freetds]
Description = MS SQL database access with Free TDS
Driver = /usr/lib/x86_64-linux-gnu/odbc/libtdsodbc.so
Setup = /usr/lib/x86_64-linux-gnu/odbc/libtdsS.so
UsageCount = 1
/etc/odbc.ini
[mssql_db1_freetds]
Description = MSSQL Server
Driver = freetds
Database = Db1
ServerName = mssql_db1_freetds
TDS_Version = 7.0
[mssql_db2_freetds]
Description = MSSQL Server
Driver = freetds
Database = Db2
ServerName = mssql_db2_freetds
TDS_Version = 7.0
/etc/freetds/freetds.conf
[global]
# TDS protocol version
; tds version = 4.2
# Whether to write a TDSDUMP file for diagnostic purposes
# (setting this to /tmp is insecure on a multi-user system)
; dump file = /tmp/freetds.log
; debug flags = 0xffff
# Command and connection timeouts
timeout = 600
connect timeout = 600
[mssql_db1_freetds]
host = 192.168.0.20
port = 1433
timeout = 600
connect timeout = 600
tds version = 7.0
text size = 20971520
[mssql_db2_freetds]
host = 192.168.0.20
port = 1433
timeout = 600
connect timeout = 600
tds version = 7.0
text size = 20971520