Irregular alerts when detecting missing events for multiple keys using Siddhi

Question

I want to detect missing events for multiple keys and the rule has two parts:

1. No event in the timeWindow after system starts - Trigger an alert
2. No event for timeWindow after an event already occured.

I have this rule which works fine for one id..

from not inputStream[id == 'ID12345'] for 20 sec 
select 'ID12345' as id, 'ID12345-GapDetection' as ruleId insert into outputStream; 
from every f1=inputStream[id == 'ID12345'] -> not inputStream[id == f1.id] for 20 sec 
select f1.id as id, 'ID12345-GapDetection' as ruleId  insert into outputStream;

However, when I add a similar rule, with the only difference being filter Id (Adding 2 rules in the system - ID12345, IDPQRST) with different rule ids.

from not inputStream[id == 'IDPQRST'] for 20 sec 
select 'IDPQRST' as id, 'IDPQRST-GapDetection' as ruleId insert into outputStream; 
from every f1=inputStream[id == 'IDPQRST'] -> not inputStream[id == f1.id] for 20 sec 
select f1.id as id, 'IDPQRST-GapDetection' as ruleId  insert into outputStream;

The output is random and not what I expect. It randomly alerts in the following ways:

1. Two correct alerts (One for each ID)
2. Alerts for either of the IDs
3. Misses the alerting completely and stops alerting any further
4. Alerts for the same ID twice

I have tried a couple of other rules too to achieve the same solution, however they all end up with the same issue. My other tried rule is:

Using sequence:

from not inputStream[id == 'ID12345'] for 20 sec 
select 'ID12345' as id, 'ID12345-GapDetection' as ruleId insert into outputStream;
from every f1=inputStream[id == 'ID12345'], not inputStream[id == 'ID12345'] for 20 sec 
select f1.id as id, 'ID12345-GapDetection' as ruleId  insert into outputStream;

This makes me wonder if this has got something to do with the way internal rule trigger works for detecting missing events within a certain time period.

I also noticed that if input events are generated at a slower rate, the alerts get triggered correctly.