As the grok parsing failed, @timestamp could not be updated based on the data in the log entry, which is why you see the default value (the current processing time).
I would also recommend moving the date and age filters to just after the grok filter. That way you can drop the events before going through the deep and useragent processing.
That is probably because the s3 input plugin reads all files in that bucket, which probably contains older data. I have not used the s3 plugin, but it looks like you might be able to exclude files/data to be read using the exclude_pattern directive.
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