expression
at some point in the past; at some stage
Used to refer to an unspecified time in the past when something began or changed, often with a sense of vagueness or nostalgia.
いつの頃からか、彼は毎朝ジョギングをするようになった。
At some point, he started jogging every morning.
いつの頃からか、この町に住みたいと思うようになった。
At some stage, I came to want to live in this town.
Similar meaning but less formal and without the 頃 nuance of 'around when'; いつの頃からか emphasizes the vagueness of the time.
A fixed phrase composed of いつ (when), の (possessive particle), 頃 (approximate time), から (from), and か (question marker), literally 'from around when?', used idiomatically to mean 'at some point in the past'.