atari
2
Have asked the same question 3 weeks ago, no answer so far.
The “bursts” you see is most likely bridgestrap from a German IP, see your /var/lib/tor/stats/bridge-stats.
Your bridge showing offline from time to time is related to not exposing your ORPort (which is highly recommended). See these 2 tickets:
Recommend not exposing OrPort for bridges (#129) · Issues · The Tor Project / Anti-censorship / Team · GitLab
webtunnel-from-source instructions close your ORPort without explaining that your bridge will seem down (#329) · Issues · The Tor Project / Web / community · GitLab
If you can use your bridge and its shown as “webtunnel: functional” when you check here: https://bridges.torproject.org/status?id=$YOURFINGERPRINT → try being patient, I’m trying too… 
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