The probable nature of these afflictions (NIV: trials) has been discussed in 1 Thessalonians 1:6 and 1 Thessalonians 2:14. As Furnish suggests,
Most likely because the converts had abandoned their former gods and religious practices...they were perceived by others as a threat to the social and political well-being of the city. This would have resulted in such difficulties as their alienation from unbelieving family members and friends; the curtailment of their opportunities to maintain, let alone to improve, their current economic and social status; the restriction of their access to the city’s political and social institutions; and their constant subjection to harassment and public insults.1
3 that no one be moved by these afflictions. For you yourselves know that we are destined for this.