When a BGP speaker receives a L3VPN prefix which target community is mismatch with local configured, then the prefixes are rejected due to lack of a valid target community and the route is not installed. 

Topology:

CE1<---->PE1<---->P<---->PE2<---->CE2

PE1 target is configured as 4-byte AS format.

#set routing-instances vpn1 vrf-target target:65001L:101

PE2 target is configured as normal format(2-bytes).

#set routing-instances vpn1 vrf-target target:65001:101

About BGP community explanation refre below link:

https://www.juniper.net/documentation/us/en/software/junos/routing-policy/topics/concept/policy-defining-bgp-communities-and-extended-communities-in-routing-policy-match-conditions.html

On PE check receive route from peer device, there is no any output.

user@PE1>show route receive-protocol bgp 192.168.1.1 table vpn1.inet.0

vpn1.inet.0: 3 destinations, 3 routes (3 active, 0 holddown, 0 hidden)

Enable bgp traceoption and clear bgp neighbor:

#set protocols bgp traceoptions file bgp-trace

#set protocols bgp traceoptions file size 100m

#set protocols bgp traceoptions flag all

user@PE1>clear bgp neighbor 192.168.1.1

Cleared 1 connections

The L3VPN prefix is received but does not get installed in the RIB and the reason of reject is "lack of a valid target community".

user@PE1>show log jw-bgp | match communit
Jun 25 09:31:20.042913 BGP SEND flags 0xc0 code Extended Communities(16): 202:65001L:101
Jun 25 09:31:20.246931 BGP RECV flags 0xc0 code Extended Communities(16): 2:65001:101
Jun 25 09:31:20.247140 bgp_rcv_nlri: 192.168.0.2:101:10.101.0.0/80 rejected due to the lack of a valid target community
Jun 25 09:31:20.247150 bgp_rcv_nlri: 192.168.0.2:101:10.101.0.0/88 rejected due to the lack of a valid target community

Check target community configuration on all PE devices and make sure they are same.