sich einschleichen
to sneak in
To go to a place secretly, quietly, and unnoticed.
Der Fuchs hat sich nachts in den Hühnerstall eingeschlichen.
The fox sneaked into the henhouse at night.

to sneak in
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to sneak in
To go to a place secretly, quietly, and unnoticed.
Der Fuchs hat sich nachts in den Hühnerstall eingeschlichen.
The fox sneaked into the henhouse at night.

'Einschleichen' (to sneak in) is a separable verb. The prefix 'ein-' separates in a main clause and goes at the end. The verb is irregular: einschleichen, schlich ein, eingeschlichen.
Ein Fehler schlich sich in die Berechnung ein.
An error crept into the calculation.
The verb consists of 'ein-' (into/in) and 'schleichen' (to move quietly and slowly). The literal meaning 'to move secretly into something' is the basis for all figurative meanings.
Die Katze schlich sich leise ins Haus ein.
The cat sneaked quietly into the house.
This verb is almost always used reflexively with 'sich'. This applies to the literal meaning (to move secretly into something) and to all figurative meanings (errors, habits).
In meinen Text hat sich ein Tippfehler eingeschlichen.
A typo crept into my text.
The preposition indicates the meaning. 'Sich in etwas (accusative) einschleichen' means to get into something unnoticed. 'Sich bei jemandem (dative) einschleichen' means to sneak one's way into someone's trust.
Ein Virus hat sich in das Computersystem eingeschlichen.
A virus has crept into the computer system.
In the figurative meaning, 'sich einschleichen' (to creep in) is very often used for negative, unnoticed developments. Typical subjects are: an error, a misunderstanding, an inaccuracy, or a bad habit.
Mit der Zeit haben sich einige schlechte Gewohnheiten in seinen Alltag eingeschlichen.
Over time, some bad habits have crept into his everyday life.
to arise
'entstehen' and 'sich einschleichen' can both describe something being there over time that was not there before. 'entstehen' is neutral and general: a plan, a problem, or an idea can 'entstehen'. 'sich einschleichen' is used more for something negative that happens slowly and almost unnoticed, such as mistakes or bad habits. It sounds as if you only noticed it late.

In den Bericht haben sich mehrere kleine Fehler eingeschlichen.
Several small mistakes have crept into the report.
Durch das Missverständnis ist im Team ein neuer Konflikt entstanden.
Because of the misunderstanding, a new conflict arose within the team.