Error when running snapshot using API and console

[anfel (arwa)]

Hi,
we are running elastichsearch 7.17 , i have noticed that all the snapshots stored were delated without any indicator .
when i tried running a new snapshot using API : PUT _snapshot/synology/daily_snapshot-15-08-23
i have 500 -inernal server error with this output

{
  "error" : {
    "root_cause" : [
      {
        "type" : "repository_exception",
        "reason" : "[synology] Could not read repository data because the contents of the repository do not match its expected state. This is likely the result of either concurrently modifying the contents of the repository by a process other than this cluster or an issue with the repository's underlying storage. The repository has been disabled to prevent corrupting its contents. To re-enable it and continue using it please remove the repository from the cluster and add it again to make the cluster recover the known state of the repository from its physical contents."`
 "status" : 500

when i verify the snapshot repository information i get the output below

what can be the cause to this problem since there wasn't any manipulation on the nodes

also , the disk availible is 16.98%
and it shows Missing primary shards on "health"

i hope i can find any help here since i am new in the administartion of elasticsearch

regards