Maybe this will make some sense
OP reports it runs at 30 - 40 degrees initial timing, let us assume 35 degrees.
Correct initial timing should be close to 15 degrees.
Camshaft operates at 1/2 crank shaft rpm = .5
The simple math
35-15=20 degrees of crank rotation
20x.5 =10 degrees of cam rotation
10 degrees of cam rotation could easily represent the timing chain has skipped a tooth on the cam sprocket.
In this situation the TDC mark on the balancer would still show to be correct but would give you a false timing condition.
If I am wrong tell me.
