I have a cube transposing a plane and just one light. The shadow casted is weird. There is something missing at the corner. When I switch to Cycles, I got the correct shadows.
Further to @moonboots' suggestion ...
In EEVEE, direct-light shadows are achieved by shadow mapping, which can give rise to artefacts where the fakery fails. 'Bias' is one of the fudge-factors made available to relieve some self-shadowing artefacts, but may introduce some undesirable side-effects of its own.. (which you can see if you read down, from the link)
Your offset shadow is one of the side-effects, if Bias is set too high for the circumstances.
The maps are constructed per shadow-casting lamp, so the adjustments can be found in the lamp's settings: