I don't know if it worked before cause I updated the EX3300 before installing them and connecting to EX4300.
I run traceoptions for lldp with flag all on the EX3300 and EX4300.
EX3300 LLDP log - https://pastebin.com/9u8x1Tnd
EX4300 LLDP log - https://pastebin.com/81MFQb3g
I think something may be wrong with below output for EX3300
Nov 28 16:39:12.077174 config Populating ifl(ge-0/1/3.0) Nov 28 16:39:12.077228 config ifl(ge-0/1/3.0) cfg found Nov 28 16:39:12.077281 config ifl(ge-0/1/3.0) dcbx_cfg not found Nov 28 16:39:12.077335 config ifl(ge-0/1/3.0) med_cfg not found Nov 28 16:39:12.077394 config ifl(ge-0/1/3.0) parent ifl index: 0 Nov 28 16:39:12.077488 lldp Populate Port TLVs: ifl ge-0/1/3.0 Nov 28 16:39:12.077610 config get the description from ifd Nov 28 16:39:12.077749 lldp No need to generate the mode change err tlv Nov 28 16:39:12.077808 rtsock the interface speed is 1000000000 for ge-0/1/3.0 Nov 28 16:39:12.077855 rtsock the interface duplexity is 2 for ge-0/1/3.0 Nov 28 16:39:12.077902 rtsock the interface capability is 47108 for ge-0/1/3.0 Nov 28 16:39:12.077947 rtsock the interface autoneg status is 0 for ge-0/1/3.0 Nov 28 16:39:12.077993 rtsock the interface media type is 2 for ge-0/1/3.0 Nov 28 16:39:12.078052 lldp Generate link aggregation TLV for ifd ge-0/1/3 parentidx 0 Nov 28 16:39:12.078107 lldp ifd ge-0/1/3 has mtu 1514 Nov 28 16:39:12.078161 lldp Deleting vlan-id TLV for trunk ifl ge-0/1/3.0 Nov 28 16:39:12.078282 lldp Populate Port-vlan-tlv: ifl ge-0/1/3.0 is-trunk yes vlan XX native-vlan no v_owner 0x1 Nov 28 16:39:12.078343 lldp Generating vlan name =XX TLV with tag = XX tagged = 1 Nov 28 16:39:12.078406 lldp Populate Port-vlan-tlv: ifl ge-0/1/3.0 is-trunk yes vlan XX native-vlan no v_owner 0x1 Nov 28 16:39:12.078478 lldp Generating vlan name =XX TLV with tag = XX tagged = 1 Nov 28 16:39:12.078541 lldp Populate Port-vlan-tlv: ifl ge-0/1/3.0 is-trunk yes vlan XX native-vlan no v_owner 0x1 Nov 28 16:39:12.078598 lldp Generating vlan name =XX TLV with tag = XX tagged = 1 Nov 28 16:39:12.078658 lldp Populate Port-vlan-tlv: ifl ge-0/1/3.0 is-trunk yes vlan XX native-vlan no v_owner 0x1 Nov 28 16:39:12.078714 lldp Generating vlan name =XX TLV with tag = XX tagged = 1 Nov 28 16:39:12.078777 lldp Populate Port-vlan-tlv: ifl ge-0/1/3.0 is-trunk yes vlan XX native-vlan no v_owner 0x1 Nov 28 16:39:12.078832 lldp Generating vlan name =XX TLV with tag = XX tagged = 1 Nov 28 16:39:12.078895 lldp Compute Pkt Buff: intf ge-0/1/3.0 port_tlvs 0x2738e0 stop_lldp_tx 0
And below you can see recuring error which generates SNMP traps on EX3300
Nov 28 16:39:50.196887 lldp LLDP packet got added to rx queue for ifl ge-0/1/3.0 Nov 28 16:39:50.197371 lldp Warning: LLDP packet validation failed Nov 28 16:39:50.631061 main: running normal priority timer queue Nov 28 16:39:50.631181 main: ran 1 timers Nov 28 16:39:50.866519 main: running normal priority timer queue Nov 28 16:39:50.867319 main: ran 1 timers Nov 28 16:39:50.874175 task_process_events_internal: recv ready for SNMP Subagent Nov 28 16:39:50.876486 task_timer_delete: SNMP Subagent_SNMP call timer <Touched> Nov 28 16:39:50.876603 task_timer_ucreate: created timer SNMP Subagent_SNMP call timer flags <> Nov 28 16:39:50.876701 task_timer_uset: timer SNMP Subagent_SNMP call timer <Touched> set to offset 6.582263 at 16:39:57.458866 Nov 28 16:39:51.240039 main: running normal priority timer queue Nov 28 16:39:51.240264 main: ran 1 timers Nov 28 16:39:51.279024 main: running normal priority timer queue Nov 28 16:39:51.279133 main: ran 1 timers Nov 28 16:39:51.548018 main: running normal priority timer queue Nov 28 16:39:51.548127 main: ran 1 timers Nov 28 16:39:51.632033 main: running normal priority timer queue Nov 28 16:39:51.632162 main: ran 2 timers Nov 28 16:39:51.738018 main: running normal priority timer queue Nov 28 16:39:51.738128 main: ran 1 timers Nov 28 16:39:51.740032 main: running normal priority timer queue Nov 28 16:39:51.740140 main: ran 1 timers Nov 28 16:39:51.931897 main: running normal priority timer queue Nov 28 16:39:51.932011 main: ran 1 timers Nov 28 16:39:52.206212 lldp LLDP packet got added to rx queue for ifl ge-0/1/3.0 Nov 28 16:39:52.206430 lldp Warning: LLDP packet validation failed Nov 28 16:39:52.355040 main: running normal priority timer queue Nov 28 16:39:52.355813 main: ran 1 timers