Strange "circuit build measurement period"

[otto otto <o815@xxxxxxxxxxx>]

I'm seeing many messages like this:

Circuit build measurement period of 902295ms is more than twice the maximum build time we have ever observed. Capping it to 295166ms.

in the log.
The system time is synchronized with ptbtime1.ptb.de via xntp and the peerstats log file shows that it is very close:
55490 14475.697 192.53.103.108 94c4 -0.002067 0.01459 0.00885

Any idea what is causing the strange "Circuit build measurement period"

Thanks.

Rainer