I've checked this ticket with the lucee latest version 5.3.10.19-SNAPSHOT with enabled the datasource option Always reset connection to default values before use.
Yes, the jTDS driver end of every transaction didn't reset the isolation level to read committed.

I run the below code, I got the same result in both mssql and jTDS driver in lucee.

If I checked the SQL profiler data, for the mssql driver end of every transaction reset the isolation level to read committed. But for jTDS driver didn't reset the isolation level to read committed.

sql profiler data for mssql driver:

sql profiler data for jTDS driver:

Only if I change isolation level within the code Lucee, to another isolation level, only then it will change it to default

Can’t understand yet why, but when JTDS driver is used, our connection is not instanceof DatasourceConnectionImpl,

so because of that, in the DatasourceConnectionPool.java connection is not reset.

Using SQL Profiler, I found that:

“SET TRANSACTION ISOLATION LEVEL READ COMMITTED”
is executed only on:

1. creation connection in admin panel

2. verify connection from admin panel

3. Once, before the very first query.

Every following query will be executed as without resetting connection.
Even if I change isolation level by executing “SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED“.