I've seen odd CPU usage on shard1 as well. Usage will sometimes spike for no reason I can work out, and when I look closely, methods that shouldn't take much time at all take an extremely long time. (My profiling once yesterday showed my rooms taking something like ~50 cpu, in one tick, to perform an operation that it typically does in under 1 CPU, and I wasn't able to work out any possible reason it could have taken so long.)
I'm not certain the problem lies anywhere other than my code. But if we're taking inventory of people who are seeing recent flakiness in CPU usage that they haven't been able to account for, count me among them.