Though I do think it likely sounds like a seal issue, I will add that it is far more preferable to mix up a specific weight of sugar, and add to the entire volume of beer, using an online calculator. Carb drops are ‘easy’, “but what worth doing is easy?” asks the homebrewer? By inputting the highest temp reached during fermentation, desired volumes of CO2 (can look up the style), and volume of beer, you can dial in your carbonation pretty accurately based on the style guidelines/calculators.
Certain styles, I do love to bottle condition, like most belgians, especially wits and strong belgians. Saisons I tend to brew so often, I rarely have the patience for bottle conditioning :?: