Since I can't reproduce this in my system but I'm really curious what's up there, I stepped a little into the calculation of this field. Although this don't solve your problem, it might bring some light into the situation.
There are 3 values from which the salable quantity is calculated: The quantity in stock (which is the sum of all sources of the stock), the reserved quantity (from orders) and the configured minimum quantity.
The formula is: quantity in stock + reserved quantity - minimum quantity
With this SQL statements you can check the situation in your database:
-- quantity in stock
select quantity from inventory_stock_[YOUR_STOCK_ID] where sku = '[YOUR_SKU]';
-- reserved quantity
select SUM (quantity) from inventory_reservation where sku = '[YOUR_SKU]';
-- configuration for minimum quantity in stock
select min_qty, use_config_min_qty from cataloginventory_stock_item
where product_id = (select entity_id from catalog_product_entity where sku = '[YOUR_SKU]');
Please run this statements for your product and share the results with us.