After adding strongly NaOH basified solution to p. brachytachys leaves getting smell that reminds ammonia. Is something wrongly done? Is heat generated by dissoving lye bad for spice?

It smells like shit dude I wouldn't be breathing that in.

If it is above 50 degrees celsius it is bad and will start degrading it. Get a cooking thermo or just know what 50 degrees feels like with your hand somehow.