Active Record transforming dates inconsistently when querying a postgresql view

I've got a rails app that is creating a view of calendar events, some of which are stored as calendar events with a starts_at column and some of which have a generated starts_at column created from a repeating schedule.

The view is a union and looks like this (simplified):

(
  SELECT
    'appointment' AS event_type,
    starts_at
  FROM
    appointments
)
UNION
(
  SELECT
    'schedule' AS event_type,
    (
      to_timestamp(
        CONCAT(
          start_date,
          ' ',
          lpad(start_hour :: text, 2, '0'),
          ':',
          lpad(start_minute :: text, 2, '0'),
          ':00.000000'
        ),
        'YYYY-MM-DD hh24:mi:ss:us'
      ) at time zone 'UTC'
    ) :: timestamp without time zone AS starts_at
  FROM
    schedule_items
)

This works fine and when I query the view in postgres I get:

 event_type  |          ends_at
-------------+----------------------------
 schedule    | 2021-10-18 08:00:00
 schedule    | 2021-11-08 09:00:00
 appointment | 2021-10-14 17:44:15.122543

These are all correct times in UTC not in the local timezone.

I wrapped an ActiveRecord model around this view (using the scenic gem to generate the view) but when I query the model, it provides a correct time for the appointment record but an incorrect time for the schedule (generated) records.

The appointment is shown at the UTC time above (current 1 hour behind the local UK timezone).

The schedule time is show at the time above plus 1 hour (in UTC) so is 2 hours ahead of UTC when cast by Active Record.

If I build a custom cast_type for the attribute I can see that it's reading the first time above as 2021-10-18 08:00:00 UTC (effectively converting it to local time but tagging as UTC) but for the appointment record it is correctly reading it as 2021-10-14 17:44:15.122566 UTC.

If I use a basic SQL query in Active Record I get the following result:

irb(main):045:0> r = ActiveRecord::Base.connection.execute('select starts_at from calendar_events')
irb(main):045:0> r[0]
=> {"starts_at"=>2021-10-18 09:00:00.000000 UTC}
irb(main):046:0> r[2]
=> {"starts_at"=>2021-10-14 17:44:15.122543 UTC}

Which is showing that the time is being parsed wrongly for the first record and correctly for the last one.

If I use the pg gem natively I get the same result as if I query using sql:

irb(main):001:0> conn = PG.connect( dbname: 'my_db' )
=> #<PG::Connection:0x00000001222d3a48>
irb(main):002:1* conn.exec('select * from calendar_events') do |result|
irb(main):003:2*   result.each do |row|
irb(main):004:2*     puts row['starts_at']
irb(main):005:1*   end
irb(main):006:0> end
2021-10-14 17:44:15.122543
2021-11-08 09:00:00
2021-10-18 08:00:00

which shows the results I'm expecting.

The datetime column types in the calendar table are the same type as used to create the datetime in the view, e.g.

starts_at timestamp without time zone

Both the rails app and the Postgres db are set to the Europe/London timezone and all timestamps are written to the db as timestamp without time zone types with the value in UTC.

I have tried any number of ways to resolve it (e.g. creating a custom cast_type for the attribute on the model, adding self.skip_time_zone_conversion_for_attributes, attribute_before_type_cast['starts_at']) none of which solve the problem that ActiveRecord appears to be converting some dates from UTC to a local time but still marking them as UTC.

So am at a bit of a loss so any suggestions anyone has would be gratefully received!