UT hit efficiency monitor: fluctuating values

UT hit efficiency monitor added in !3925 (merged) Moore!3484 (merged) is showing instabilities when running in nightlies.

For example using the reference update Moore!4811 (merged) (linked to Moore!4522 (merged) which only causes renaming of counters):

Original values

PrForwardTrackingVelo_a7f67b46         INFO Number of counters : 10
 |    Counter                                      |     #     |    sum     | mean/eff^* | rms/err^*  |     min     |     max     |
 | "Accepted input tracks"                         |       100 |      13744 |     137.44 |
 | "Created long tracks"                           |       100 |       6763 |     67.630 |
 | "Input tracks"                                  |       100 |      14379 |     143.79 |
 | "Number of candidate bins per track"            |     13744 |     153255 |     11.151 |     18.095 |      0.0000 |      129.00 |
 | "Number of complete candidates/track 1st Loop"  |     11993 |       7410 |    0.61786 |    0.68099 |      0.0000 |      5.0000 |
 | "Number of complete candidates/track 2nd Loop"  |      6367 |        544 |   0.085441 |    0.29164 |      0.0000 |      3.0000 |
 | "Number of x candidates per track 1st Loop"     |     11993 |      25778 |     2.1494 |     2.8115 |
 | "Number of x candidates per track 2nd Loop"     |      6367 |      35938 |     5.6444 |     9.6174 |
 | "Percentage second loop execution"              |     11993 |       6367 |    0.53089 |
 | "Removed duplicates"                            |       100 |        392 |     3.9200 |

Changed values:

PrForwardTrackingVelo_a7f67b46         INFO Number of counters : 10
 |    Counter                                      |     #     |    sum     | mean/eff^* | rms/err^*  |     min     |     max     |
 | "Accepted input tracks"                         |       100 |      13747 |     137.47 |
 | "Created long tracks"                           |       100 |       6731 |     67.310 |
 | "Input tracks"                                  |       100 |      14380 |     143.80 |
 | "Number of candidate bins per track"            |     13747 |     153312 |     11.152 |     18.098 |      0.0000 |      129.00 |
 | "Number of complete candidates/track 1st Loop"  |     11995 |       7391 |    0.61617 |    0.68198 |      0.0000 |      5.0000 |
 | "Number of complete candidates/track 2nd Loop"  |      6387 |        540 |   0.084547 |    0.28924 |      0.0000 |      3.0000 |
 | "Number of x candidates per track 1st Loop"     |     11995 |      25782 |     2.1494 |     2.8112 |
 | "Number of x candidates per track 2nd Loop"     |      6387 |      36233 |     5.6729 |     9.6398 |
 | "Percentage second loop execution"              |     11995 |       6387 |    0.53247 |
 | "Removed duplicates"                            |       100 |        393 |     3.9300 |

Needs to be investigated @peilian @zhijiew

FYI @jonrob