The phrase "plausible reason" means having a sensible and believable explanation for something. It implies having a logical and reasonable justification or explanation that people are likely to accept. Full definition
Now, the only remotely plausible reason for giving him a renewed contract, albeit for pennies, would be because he has finally turned a corner and might actually play a season. (justarsenal.com)
Each person should be able to come up with at least a couple of plausible reasons for failure. (jasonzweig.com)
It is such a complicated process that for every suggested treatment technique, there are an equal number of veterinarians who give plausible reasons why that technique should not be performed. (2ndchance.info)