Below logs are generated.

# run show log messages | last 10
Jun 19 16:07:36 <snip> fpc2 PIC 2 optic modules in port 8 have been disabled since ambient temperature is over threshold
Jun 19 16:07:43 <snip> fpc2 CMIC(2/2) link 8 SFP laser bias current low alarm set
Jun 19 16:07:43 <snip> fpc2 CMIC(2/2) link 8 SFP output power low alarm set
Jun 19 16:07:43 <snip> fpc2 CMIC(2/2) link 8 SFP receive power low alarm set
Jun 19 16:07:43 <snip> fpc2 CMIC(2/2) link 8 SFP laser bias current low warning set
Jun 19 16:07:43 <snip> fpc2 CMIC(2/2) link 8 SFP output power low warning set
Jun 19 16:07:43 <snip> fpc2 CMIC(2/2) link 8 SFP receive power low warning set
Jun 19 16:11:46 <snip> fpc2 CMIC(2/2) link 8 SFP receive power low alarm cleared
Jun 19 16:11:46 <snip> fpc2 CMIC(2/2) link 8 SFP receive power low warning cleared

From the logs, the FPC2 PIC 2 optic modules in port 8 have been disabled since ambient temperature is over threshold.

The part number of the port 8 is 740-021309, which is commercial grade and not supported by SRX Junos version 12.1 , but by 12.3. The supported SFP Part number is ended w/ Xxx-xxxx80, for example, 740-031980

Please refer to the document below to find right SFP for 12.1.

http://www.juniper.net/techpubs/en_US/release-independent/junos/information-products/topic-collections/hardware/srx-series/srx-transceivers/srx-transceiver-guide.pdf

So we may replace the SFP optics with P/N 740-031980 or upgrade the version to 12.3 to resolve this issue.