Hmm... How far are you, what is the last mission you've completed? and have you spoken to all the yellow chat bubbles in Fort Tarsis as it triggers more to unlock missions before you can get access to the other Strongholds. Since there is 4 in total after the story is complete.
Tyrant Mine
Temple of Scar
Heart of Rage
Sunken Cell
"The access to first Strongholds is unlocked automatically after progressing in the main story - you need to complete a story mission "Finding Old Friends" in which you visit the hideout of Princess Zhim."
"After the return to Fort Tarsis, you'll begin conversations with Owen, Haluk, and Faye. Then, you need to meet with Tassyn to give your report from the expedition. Tassyn will tell you about new, more difficult contracts that you can undertake from now on."