I’m very sorry for the time it has taken to respond to your reply.
I’ve used your example with a few changes:
// date starting the week of loaded treasure bag
$treasure_bag_date = get_sub_field('treasure_bag_date', 85);
$last_week = $treasure_bag_date-6;
$next_week = $treasure_bag_date+6;
<tr <?php if( ($treasure_bag_date >= $last_week) && ($treasure_bag_date <= $next_week) ){ echo "id='active_week'"; }?>>
The code is echoing all the weeks.
Here is an example https://www.gymbaroomteliza.com/treasure_bag/