Not sure if this is related, but sreg(1) should not be considered an
asynchronous register, only sreg(0). You may have to split them up
into separate signals to handle it. You will also want to make sure
(constrain) that sreg(0) does not get replicated for fanout (e.g. if
sreg(1) gets replicated enough due to high fanout, that can ripple to
replicating sreg(0).)

Is the output from your syncrhonizer going anywhere? If not it may be
getting optimized away, thus prompting the warnings.

Andy