Branches get randomly "crossed out" for no apparent reason

### Version report

Jenkins and plugins versions report:

```
Jenkins: 2.289.1
OS: Linux - 4.14.232-176.381.amzn2.x86_64
---
jjwt-api:0.11.2-9.c8b45b8bb173
sshd:3.0.3
cloudbees-folder:6.15
trilead-api:1.0.13
durable-task:1.37
antisamy-markup-formatter:2.1
handlebars:3.0.8
structs:1.23
workflow-cps:2.92
workflow-step-api:2.23
token-macro:2.15
build-timeout:1.20
momentjs:1.1.1
credentials:2.5
workflow-job:2.41
plain-credentials:1.7
ssh-credentials:1.19
mailer:1.34
credentials-binding:1.26
scm-api:2.6.4
workflow-api:2.46
timestamper:1.13
caffeine-api:2.9.1-23.v51c4e2c879c8
script-security:1.77
workflow-basic-steps:2.23
plugin-util-api:2.3.0
font-awesome-api:5.15.3-3
jsch:0.1.55.2
popper-api:1.16.1-2
jquery3-api:3.6.0-1
gradle:1.36
bootstrap4-api:4.6.0-3
pipeline-milestone-step:1.3.2
snakeyaml-api:1.29.1
git-client:3.7.2
jackson2-api:2.12.3
popper2-api:2.5.4-2
bootstrap5-api:5.0.1-2
git-server:1.9
echarts-api:5.1.2-2
display-url-api:2.3.5
pipeline-input-step:2.12
workflow-support:3.8
checks-api:1.7.0
branch-api:2.6.4
junit:1.50
matrix-project:1.19
pipeline-stage-step:2.5
resource-disposer:0.16
ws-cleanup:0.39
ant:1.11
workflow-durable-task-step:2.39
pipeline-graph-analysis:1.11
command-launcher:1.6
jdk-tool:1.5
bouncycastle-api:2.20
ace-editor:1.1
workflow-scm-step:2.13
pipeline-rest-api:2.19
blueocean-web:1.24.7
apache-httpcomponents-client-4-api:4.5.13-1.0
generic-webhook-trigger:1.74
pipeline-stage-view:2.19
pipeline-build-step:2.13
pipeline-model-api:1.8.5
aws-credentials:1.29
pipeline-model-extensions:1.8.5
workflow-cps-global-lib:2.21
blueocean-commons:1.24.7
workflow-multibranch:2.26
ec2-fleet:2.3.2
pipeline-stage-tags-metadata:1.8.5
pipeline-model-definition:1.8.5
lockable-resources:2.11
blueocean-rest:1.24.7
workflow-aggregator:2.6
blueocean-jwt:1.24.7
okhttp-api:3.14.9
github-api:1.123
git:4.7.2
github:1.33.1
github-branch-source:2.11.1
pubsub-light:1.16
pipeline-github-lib:1.0
ssh-slaves:1.32.0
favorite:2.3.3
matrix-auth:2.6.7
pam-auth:1.6
ldap:2.7
email-ext:2.83
dashboard-view:2.17
authentication-tokens:1.4
configuration-as-code:1.51
ansicolor:1.0.0
ssh-agent:1.23
msbuild:1.30
config-file-provider:3.8.0
slack:2.48
nodejs:1.4.0
copyartifact:1.46.1
htmlpublisher:1.25
run-condition:1.5
pipeline-npm:0.9.2
javadoc:1.6
blueocean-config:1.24.7
maven-plugin:3.12
conditional-buildstep:1.4.1
handy-uri-templates-2-api:2.1.8-1.0
parameterized-trigger:2.41
jquery:1.12.4-1
jenkins-design-language:1.24.7
git-parameter:0.9.13
role-strategy:3.1.1
publish-over:0.22
publish-over-ssh:1.22
ivy:2.1
ssh:2.6.1
variant:1.4
sse-gateway:1.24
aws-java-sdk:1.11.995
cloudbees-bitbucket-branch-source:2.9.9
blueocean-pipeline-scm-api:1.24.7
blueocean-core-js:1.24.7
blueocean-rest-impl:1.24.7
jobConfigHistory:2.28.1
blueocean-pipeline-api-impl:1.24.7
blueocean-bitbucket-pipeline:1.24.7
blueocean-github-pipeline:1.24.7
blueocean-git-pipeline:1.24.7
blueocean-dashboard:1.24.7
blueocean-personalization:1.24.7
blueocean-display-url:2.4.1
blueocean-events:1.24.7
blueocean-pipeline-editor:1.24.7
blueocean-i18n:1.24.7
blueocean-autofavorite:1.2.4
blueocean:1.24.7
docker-commons:1.17
docker-workflow:1.26
pipeline-aws:1.43
artifactory:3.11.4
pipeline-utility-steps:2.8.0
data-tables-api:1.10.25-1
forensics-api:1.1.0
code-coverage-api:1.4.0
cobertura:1.16
nunit:0.27
s3:0.11.7
file-operations:1.11
rebuild:1.32
http_request:1.9.0
content-replace:1.6.0
extended-choice-parameter:0.82
theme-manager:0.6
material-theme:0.3.3
job-dsl:1.77
build-monitor-plugin:1.12+build.201809061734
gitlab-api:1.0.6
gitlab-branch-source:1.5.8
```

- What Operating System are you using (both controller, and any agents involved in the problem)?

```
ubuntu 18
```

### Reproduction steps

- Create a new multibranch pipeline
- Configure Gitlab branch source
- Add "filter by name (with wildcards) - develop master MR* dev2 dev4 qa prod5
- Save
- Branches are discovered and builds are started correctly

### Results

Expected result:

Returning to the pipeline UI after some time has passed will still show the same branches as discovered and open, unless they have been removed from Gitlab.

Actual result:

Come back later and see that most discovered branches are "crossed out". Seems like this happens with branches that do not have activity for a while. Branch discovery strategy is set to "all branches" so branches should not be filtered out even if they are filed as MRs (regardless, they are not filed as MRs).

A push to one of these branches re-opens it and starts a build (after a delay of about 10-20 seconds).

Running a manual iscan re-opens all the closed branches.

It looks like some sort of behavior that closes discovered branches on Jenkins if there has not been activity on them for a while, but I've been unable to see any setting related to this.