Hello Vincent, I reported this bug upstream [1] and got an reply that it is fixed in version 1.10.3 It seems that it isn’t a ppc specific bug, instead it is a general problem with (old) single core CPU. (a quick fix is mentioned in the reply too)
Thank you for your help. Regards, Markus [1] https://github.com/brndnmtthws/conky/issues/290
