GFFCompare ".tracking" file has zero value in<FPKM>|<TPM>|<cov> columns

[Miracle-Yao]

Hello, When I compared single merged.stringtie.assembly.gtf (generated by stringtie merge function) file with known annotation gtf file, I found each line in .tracking has zero value in <FPKM>|<TPM>| columns，how can I got this information? An example:

qJ:<gene_id>|<transcript_id>|<num_exons>|<FPKM>|<TPM>|<cov>|<len>
q1:MSTRG.1|MSTRG.1.1|3|0.000000|0.000000|0.000000|3357

Thanks