Por favor, consulte a página manpage de exports(5) :
Machine Name Formats
NFS clients may be specified in a number of ways:
[...]
IP networks
You can also export directories to all hosts on an IP (sub-) network
simultaneously. This is done by specifying an IP address and netmask pair
as address/netmask where the netmask can be specified in dotted-decimal
format, or as a contiguous mask length. For example, either
'/255.255.252.0' or '/22' appended to the network base IPv4 address
results in identical subnetworks with 10 bits of host. [...]
Wildcard characters generally do not work on IP addresses, though they
may work by accident when reverse DNS lookups fail.
wildcards
Machine names may contain the wildcard characters * and ?, or may contain
character class lists within [square brackets]. This can be used to make
the exports file more compact; for instance, *.cs.foo.edu matches all
hosts in the domain cs.foo.edu. As these characters also match the dots
in a domain name, the given pattern will also match all hosts within any
subdomain of cs.foo.edu.
Isso significa simplesmente que você está configurando errado na linha
/myshare 192.168.1.*(rw,sync,no_subtree_check)
Caracteres curinga podem ser usados em nomes de host, para especificar redes IP, você precisa usar endereços IP com pontos decimais e um tamanho de sub-rede opcional. A história inversa de pesquisa de IP acima poderia explicar por que funcionou para um endereço específico.