Error about endless loop or blocked at the process element

In the log file of our project we have an error:

05:43:46 ERROR [ch.ivyteam.ivy.process.engine.internal] [pool-1-thread-3] [executionContext=SYSTEM] 
  The following requests seems to loop endless or are blocked:
    1372F90D43E65C7E/1372F90D43E65C7E-f11/TaskA.ivp(17109512.20863568.0.0) [Executing since 26 minutes. At the moment the process element 138C2B0B699D731A-f3-io2 of alag_bpmp/alag_ria$5 is executed.
    Functional Processes/writeLeaseApplication.mod/137C0D1EEFE8D1EC-f0.callExternalSub(17109512.20863568.0.1) [Executing since 26 minutes. At the moment the process element 138C2B0B699D731A-f3-io2 of alag_bpmp/alag_integration$5 is executed.
    1372F90D43E65C7E/1372F90D43E65C7E-f11/TaskA.ivp(17210747.21050632.0.0) [Executing since 26 minutes. At the moment the process element 138C2B0B699D731A-f3-io2 of alag_bpmp/alag_ria$5 is executed.
    Functional Processes/writeLeaseApplication.mod/137C0D1EEFE8D1EC-f0.callExternalSub(17210747.21050632.0.1) [Executing since 26 minutes. At the moment the process element 138C2B0B699D731A-f3-io2 of alag_bpmp/alag_integration$5 is executed.
    1372F90D43E65C7E/1372F90D43E65C7E-f11/TaskA.ivp(17215488.21010717.0.0) [Executing since 27 minutes. At the moment the process element 1431D58E52392188-f3-io2 of alag_bpmp/alag_ria$5 is executed.
    Functional Processes/CRMInterface/reportStatusChangeToCRM.mod/142DA7A7B5BF8FCC-f0.callExternalSub(17215488.21010717.0.1) [Executing since 22 minutes. At the moment the process element 1431D58E52392188-f3-io2 of alag_bpmp/alag_integration$5 is executed.
    1372F90D43E65C7E/1372F90D43E65C7E-f11/TaskA.ivp(17215626.21053445.0.0) [Executing since 26 minutes. At the moment the process element 1431D58E52392188-f3-io2 of alag_bpmp/alag_ria$5 is executed.
    Functional Processes/CRMInterface/reportStatusChangeToCRM.mod/142DA7A7B5BF8FCC-f0.callExternalSub(17215626.21053445.0.1) [Executing since 20 minutes. At the moment the process element 1431D58E52392188-f3-io2 of alag_bpmp/alag_integration$5 is executed.
    1372F90D43E65C7E/1372F90D43E65C7E-f11/TaskA.ivp(17611524.21053061.0.0) [Executing since 26 minutes. At the moment the process element 1431D58E52392188-f3-io2 of alag_bpmp/alag_ria$5 is executed.

It happened when we call external sub, it's seem that the sub process could not be ended. We are using AxonIvyEngine5 and this error happened when the server run with high load of request. Have you ever seen similar cases? And what conditions would make Ivy throw "endless loop error"? How can we prevent this error?