This is the 965th most frequent Hungarian word.
gyakori
Frequent.
Here, 'gyakori' is an adjective describing the noun 'tevékenység' (activity), indicating that hiking happens often in that context.
A túrázás gyakori tevékenység a hegységben élők számára.
Hiking is a frequent activity for those living in the mountains.
In this sentence, 'gyakori' again functions as an adjective to qualify 'probléma' (problem), conveying that such cancellations occur regularly.
Gyakori probléma az eső miatt elmaradó rendezvény.
The event being canceled due to rain is a frequent problem.
The term 'gyakori' is used to characterize 'növekedése' (increase), suggesting that it happens many times during this period.