A player may begin with a lower-quality adaptive stream and move up as it measures the connection; a soft start is different from a picture that stays blurred.
Why this happens
Some adaptive streams offer several quality versions of the same programme. The player chooses between them as playback begins and the connection settles. That can produce a short period of softer detail before the picture sharpens, even though the television and subscription have not changed. A fixed-quality stream behaves differently: there may be no higher version for the player to select. The first few seconds alone are therefore a poor way to judge the whole session.
Watch the same source for a little longer and look for a clear change rather than repeatedly opening different channels. If the player exposes stream information, compare the video dimensions near startup with those shown once playback is steady. A picture that remains soft while motion is smooth points toward the selected source or encoding; a picture that repeatedly drops quality during busy household use suggests a different comparison. Avoid forcing a maximum quality setting before finding out whether the stream actually supplies several versions.
A useful way to work through it
Play one source without channel hopping and note when the picture settles.
Compare the reported source dimensions at startup and after steady playback, if available.
If detail stays poor, compare another source version while leaving the device and output settings unchanged.